This briefing has ended. Read the latest developments in the coronavirus outbreak here.

U.S. plans to swiftly turn back people entering from Mexico illegally.

The Trump administration plans to immediately turn back all asylum seekers and other foreigners attempting to enter the United States from Mexico illegally, saying the nation cannot risk allowing the coronavirus to spread through detention facilities and Border Patrol agents, four administration officials said.

The administration officials said the ports of entry would remain open to American citizens, green-card holders and foreigners with proper documentation. Some foreigners would be blocked, including Europeans currently subject to earlier travel restrictions imposed by the administration. The points of entry will also be open to commercial traffic.

But under the new rule, set to be announced in the next 48 hours, Border Patrol agents would immediately return anyone to Mexico — without any detainment and without any due process — who attempts to cross the southwestern border between the legal ports of entry. The person would not be held for any length of time in an American facility.

Although they advised that details could change before the announcement, administration officials said the measure was needed to avert what they fear could be a systemwide outbreak of the coronavirus inside detention facilities along the border. Such an outbreak could spread quickly through the immigrant population and could infect large numbers of Border Patrol agents, leaving the southwestern border defenses weakened, the officials argued.

Administration officials say many of the migrants who cross the border are already sick or lack sufficient documents detailing their medical history.

Confirmed cases of the virus in Mexico stand at 82, compared with around 5,600 in the United States and more than 470 in Canada. But Mr. Trump has suggested closing the border many times in the past, hoping to crack down on illegal immigration and press Mexico to do more to curb the northward flow of migrants.

Deaths in U.S. pass 100 as the coronavirus reaches all 50 states.

At least 100 deaths in the United States have now been linked to the coronavirus, according to a New York Times database that is tracking and mapping every known case in the country as more people are tested. On Tuesday evening, West Virginia became the 50th state to report a case.

The 101 deaths, all announced in the last three weeks, came as the number of known coronavirus cases in the United States soared past 5,600 on Tuesday. Hundreds more people are learning they have the illness each day, including more than 800 diagnoses on both Monday and Tuesday, as the nation’s testing capacity has grown significantly and as the virus spreads.

About half the country’s reported deaths have been in Washington State, including at least 30 linked to a long-term care facility in the Seattle suburb of Kirkland. Residents of at least two more long-term care facilities in Washington, plus others in Kansas and South Carolina, have also died, underscoring the elevated risks for older adults and people with underlying health problems.

Most of those who have died from the virus have been in their 60s or older, and several have been in their 90s. But other patients who died have been younger, including a corrections worker in New York City in his 50s and a man from the Seattle area in his 40s.

Though Washington, New York and California account for about two-thirds of the country’s coronavirus deaths, 14 other states have reported at least one fatal case of the illness.

The E.U. barred most travelers from outside the bloc for 30 days.

European leaders voted Tuesday to close off at least 26 countries to nearly all visitors from the rest of the world for at least 30 days in a bid to arrest the spread of the coronavirus, starting a long stretch of isolation like nothing in modern European history outside wartime.

The travel ban — which Britain did not plan to participate in — represented the first coordinated response to the epidemic by the European Union.

Special exceptions would be made for European citizens and residents coming home, although some countries were asking them to self-isolate for two weeks, in some cases away from their families. Medical professionals and scientists would be exempt from the measures, as would people living in one European country and commuting to another for work.

It was the most dramatic action on a day that the Continent continued to grapple with the growing coronavirus crisis, as some countries restricted the movements of their citizens and others proposed relief packages to try to contain the economic damage.

Spain’s prime minister, Pedro Sánchez, announced a €200 billion relief aid package on Tuesday — equivalent to one-fifth of Spain’s gross domestic product — to help alleviate the economic impact of the pandemic. At least 491 people have died in the country and there have been 11,178 confirmed cases.

The death of Spain’s youngest known victim so far, Francisco García, 21, struck a chord with the nation. Mr. García, a soccer coach from Málaga, did not know he had an underlying condition when he went to the hospital. But he was soon hit with a double dose of bad news: He was infected with the coronavirus and he had leukemia. He died on Sunday.

In France, the government announced a relief package that would include postponing or slashing taxes, a government guarantee of loans for companies, and more than $1.1 billion for small businesses and independent contractors.

Germany raced to bring home thousands of its citizens, its government spending more than $55 million on logistics and flights as nations tighten their borders and travel becomes exceedingly difficult. Turkey reported its first death caused by the coronavirus. And the Russian government prepared to block most foreigners from entering the country starting Wednesday. Moscow banned events of more than 50 people and ordered schools closed starting Saturday.

In France, the sanctuary in Lourdes, a major Catholic pilgrimage site that is visited by millions every year, was closed until further notice. And in Britain, Queen Elizabeth II planned to leave for Windsor Castle for Easter on Thursday, a week earlier than planned, and the palace announced that she would likely remain there after the holiday ends.

After weeks of being cut off from the outside world, the contestants on the German version of “Big Brother” were told about the pandemic in a special live show on Tuesday. Several of the 14 contestants, who had been sequestered since Feb. 6, erupted into sobs when the host explained that the disease had reached Europe and showed news clips of recent events.

The Trump administration wants to send cash directly to Americans.

As the growing economic toll of the coronavirus became clearer, the White House said it supported the idea of sending cash payments directly to Americans as part of a broader $850 billion stimulus proposal that Treasury Secretary Steven Mnuchin discussed on Tuesday with Republicans on Capitol Hill.

It was a shift in priority for the administration, which has been advocating a payroll tax cut, and it came as the coronavirus ground large swaths of the economy to a halt. Mr. Mnuchin noted that the effects of a payroll tax cut would take months to reach people.

He later told senators that about $250 billion of the stimulus plan would cover the cost of sending checks to Americans to replace about two weeks of their wages, according to people familiar with his proposal. The checks would go out by the end of April, and could be repeated if the crisis persists, said the people, who spoke on condition of anonymity.

After the session, Mr. Mnuchin declined to publicly put a dollar figure on the payments, telling reporters only that “it is a big number.” Earlier at the White House, he said the proposal would exclude the highest earners, like those making $1 million or more.

Mr. Trump, who spent his morning heckling governors on Twitter, struck a tone of coordination and cooperation in the briefing room. He said many of his administration’s actions have been intended to bolster the economy.

Mr. Mnuchin also said that Mr. Trump had instructed him to allow taxpayers to put off paying income taxes that are due April 15 for 90 days without penalty or interest.

The Trump administration is also supporting a request for $50 billion in economic relief for the airline industry as part of the broader package.

The White House moved as the Federal Reserve announced on Tuesday that it would try to keep credit flowing to households and businesses by buying up short-term promissory notes issued by companies, known as commercial paper.

“This Fed facility ensures that companies can get the overnight funding they need to meet short-term obligations like payroll,” said Ernie Tedeschi, policy economist at Evercore ISI.

There were signs of support in Congress for the idea of sending direct payments to ordinary people. A group of Senate Democrats, led by Michael Bennet of Colorado, Cory Booker of New Jersey and Sherrod Brown of Ohio, had earlier proposed legislation to send as much as $4,500 to nearly every adult and child in the United States this year, as part of a sustained government income-support program.

The virus could possibly survive in the air, a new study suggests.

The coronavirus can live for three days on some surfaces, like plastic and steel — though the amount of viable virus decreases sharply over this time — suggests a new study, published on Tuesday in the New England Journal of Medicine.

Experts say the risk of consumers getting infected from touching those materials is still low, though they offered additional warnings about how long the virus could survive in the air, which may have important implications for medical workers.

When the virus becomes suspended in droplets smaller than five micrometers — known as aerosols — it can stay suspended for about 30 minutes, before drifting down and settling on surfaces where it can linger for hours, the researchers said. The finding is inconsistent with the World Health Organization’s position that the virus is not transported by air.

The new study also suggests that the virus can survive up to 24 hours on cardboard packages, though it disintegrates over the course of a day — meaning cardboard packages that arrive in the mail would have only low levels of the virus unless the delivery person has coughed or sneezed on it or has handled it with contaminated hands.

Another study, the largest to date of children and the virus, has found that while most develop mild or moderate symptoms, a small percentage — especially babies and preschoolers — can become seriously ill. Children account for the smallest percentage of the tens of thousands of infections identified globally.

The study, published online in the journal Pediatrics, looked at more than 2,000 ill children across China, where the pandemic began. It provides a clearer portrait of how the youngest patients are affected by the virus, knowledge that experts say can help influence policies like school closures, hospital preparedness and the deployment of an eventual treatment and vaccine.

Flights are canceled in Chicago as U.S. travel woes compound.

The Federal Aviation Administration closed the lone air traffic control tower at Chicago Midway International Airport on Tuesday after three technicians at the facility tested positive for the coronavirus, an agency spokesman said.

Nearly all flights scheduled to take off from or land at the airport after 6 p.m. were canceled, according to the airport’s website, which indicated that more than 177 flights had been halted in the last 24 hours. The tower closure was described by the F.A.A. as temporary, but it was unclear when the airport would resume normal operations. The city’s more popular airport, O’Hare, sees more than four times the amount of traffic that Midway does each day.

Most airlines have announced cuts to international flights because of a sudden drop in demand, and airlines have asked the government for a bailout and banks for billions in loans.

And across the country, public transit agencies have struggled amid low ridership and health concerns from their employees and customers. New York City’s public transportation system, the largest in North America, is seeking a $4 billion federal bailout as the pandemic set off an extraordinary free fall in ridership.

In a letter on Tuesday to New York’s congressional delegation, the Metropolitan Transportation Authority, which runs the city’s subway and buses and two commuter railroads, said that subway ridership had plunged 60 percent and bus ridership had fallen 49 percent on Monday compared with the same day last year.

Bus service in Detroit was halted after drivers, fearing for their safety, balked at leaving their garages. Glenn Tolbert, the president of Amalgamated Transit Union Local 26, which represents the Detroit bus drivers, said that some drivers had reported to work early in the morning and found that the buses were not adequately cleaned.

He also said restrictions on businesses and hospitals had deprived the drivers of places on their routes to visit restrooms and wash their hands.

“We just didn’t feel that the city, although they were making an effort, was doing enough to protect us and the public,” Mr. Tolbert said.

Parts of the U.S. could run out of hospital beds.

A new Harvard analysis shows that many parts of the United States would have far too few hospital beds if the new coronavirus continues to spread widely and nothing is done to expand capacity.

In 40 percent of markets around the country, hospitals would not be able to make enough room for all Covid-19 patients even if they were completely emptied of other patients. That statistic assumes that 40 percent of all adults become infected with the virus over 12 months, a scenario described as “moderate” by the team behind the calculations.

Around the country, hospitals have begun canceling elective operations and speeding patients with less critical ailments home, to make beds available for possible coronavirus patients.

Yet the Harvard estimates suggest that much more may be needed. In hard-hit Italy, hospitals have resorted to rationing care for older patients who are severely ill with the virus.

[Read: My life on Italy’s coronavirus frontlines, and in quarantine.]

What is social distancing? And how do you do it?

There are many misunderstandings about social distancing. Can you leave your home? Can you go to the grocery store? We compiled some helpful hints about how to keep safe.

Find more coverage on how coronavirus is impacting your day-to-day life here.

Stocks on Wall Street rebounded after another emergency step by the Fed.

Stocks rose on Tuesday, lifted by the latest emergency measure from the Federal Reserve to keep money flowing through the economy and talk of further stimulus efforts in Washington. They made up some of the ground lost on Monday in the sharpest drop since the coronavirus outbreak began.

The S&P 500 rose about 6 percent after a 12 percent plunge on Monday, its steepest drop since 1987.

But the tone of the trading was tentative. The best-performing parts of the market were traditionally safe and staid sectors like utilities and consumer staples, where risk-averse investors hide during trying economic times. Reflecting concern about the global economy, oil prices fell.

There are few historical parallels for the market shock waves created by the outbreak. From still-closed factories in China to Western nations where millions of people are living in a state of semi-house arrest, most of the engines that keep the global economy aloft have sputtered to a halt at the same time.

New York City considers a shelter-in-place order as public life is curtailed.

Mayor Bill de Blasio of New York City said that residents should prepare for the possibility of a “shelter in place” order to be announced in the next 48 hours, as the number of confirmed coronavirus cases in New York City neared 1,000.

Mr. de Blasio said that a decision on such an order, which would require coordination between the city and New York State, had not been made. But he said he believed that kind of recommendation, which is in place in San Francisco, would be “the right guidance.”

New York City has already come to a halt, but a “shelter in place” recommendation would be a major escalation in restrictions on public life. The mayor did not elaborate on what such an order would look like in practice.

Mr. de Blasio said the city was also rushing to add more hospital beds.

Voting went ahead in Florida, Illinois and Arizona, but not Ohio.

With states postponing upcoming primaries to avoid congregating during the coronavirus pandemic, Democratic National Committee Chairman Tom Perez on Tuesday urged the states left to vote to conduct all vote-by-mail contests.

“In order to ensure the voices of voters are heard, the DNC is urging the remaining primary states to use a variety of other critical mechanisms that will make voting easier and safer for voters and election officials alike,” Mr. Perez said. “The simplest tool is vote by mail, which is already in use in a number of states and should be made available to all registered voters.”

Voters did not go to the polls Tuesday in Ohio, where the presidential primary was postponed after state officials declared a public health emergency — but the primaries in Arizona, Florida and Illinois went ahead as scheduled. Former Vice President Joseph R. Biden Jr. won all three states, according to The Associated Press.

Maryland became the fifth state to postpone its primary election, when Gov. Larry Hogan announced on Tuesday that the April 28 primary would instead be held on June 2.

In states that went ahead with their elections — even after the White House urged people to avoid gatherings of more than 10 people — officials took steps to try to keep voters and poll workers safe. In Arizona, some counties offered curbside pickup outside precincts Tuesday so that voters could turn in their ballots without having to enter crowded polling sites.

The outgoing White House chief of staff, Mick Mulvaney, is in self-quarantine.

Mick Mulvaney, the outgoing acting White House chief of staff, is in self-quarantine in his home state of South Carolina, after his niece, with whom he shares an apartment in Washington, fell ill and is awaiting test results, according to four people familiar with the matter.

Mr. Mulvaney took a test for the coronavirus last week and the results were negative, according to one of the people familiar with the matter. But the results of the test that his niece, Maggie, took are not back yet, the person said.

Mr. Mulvaney’s niece is a professional fund-raiser who works on a team led by Kimberly Guilfoyle, the head of the Trump Victory finance effort. Ms. Mulvaney, Ms. Guilfoyle and others were all at Mar-a-Lago, President Trump’s private club, the weekend of March 6 for a series of events, including a Republican National Committee fund-raising retreat and Ms. Guilfoyle’s 50th birthday party.

The same weekend, President Jair Bolsonaro of Brazil dined with Mr. Trump. One of Mr. Bolsonaro’s aides who was present has since tested positive for the coronavirus.

Cases spike in Brazil as it reports its first death

Health officials in Brazil reported a sharp rise in confirmed cases and the country’s first coronavirus-related death on Tuesday. The 62-year-old patient who died had diabetes and high blood pressure, and was not among the confirmed cases health officials were tracking.

As of Tuesday, officials said, Brazil had 290 confirmed cases and suspected several thousand more.

Brazil and several of its neighbors announced new actions to fight the spread of the virus. Airlines suspended international flights and local officials curbed train and bus service. Following Colombia’s lead, Brazil closed its border with Venezuela.

President Nicolás Maduro of Venezuela, who declared a nationwide quarantine on Monday, requested a $5 billion assistance package from the International Monetary Fund, an institution he has previously disparaged.

Read the latest developments in the coronavirus outbreak here.

Reporting was contributed by Apoorva Mandvilli, Eric Lipton, Ben Protess, Monica Davey, Zolan Kanno-Youngs, Michael D. Shear, Maggie Haberman, Ernesto Londoño, Pam Belluck, Michael Cooper, Katie Rogers, Karen Zraick, Anton Troianovski, Matthew Haag, Sean Plambeck, Patricia Mazzei, Adeel Hassan, Kate Taylor, Catie Edmondson, Christina Goldbaum, Reid J. Epstein, Steven Lee Myers, Margot Sanger-Katz, Sarah Kliff, Alicia Parlapiano, Alan Rappeport, Emily Cochrane, Melissa Eddy, Raphael Minder, Aurelien Breeden, Marc Santora, Helene Cooper, Megan Specia, Jonathan Martin, Richard C. Paddock, Maya Salam, Neil Vigdor, Nick Corasaniti, Stephanie Saul, Tiffany May, Patricia Cohen, Jeffrey Gettleman, Suhasini Raj, Karan Deep Singh, Kai Schultz, Niki Kitsantonis, Jim Tankersley, Nicholas Bogel-Burroughs and Mitch Smith.