More than 400 African migrants seeking to travel to Italy on two vessels are feared drowned after going missing days ago in the Mediterranean, a UN official hassaid.

As Italy began the evacuation from Lampedusa of the 3,000 Tunisians who have reached the island since the collapse of the Tunisian government in January, another 362 migrants arrived in leaking vessels by mid-Sunday.

But two boats that reportedly set out from Libya on 22 and 25 March, one carrying 335 Eritreans and the other 68 Eritreans and Ethiopians, have disappeared.

"We are urging the coastguard to carry on searching since even after 20 days at sea, some people can survive," said Laura Boldrini, a UN spokeswoman.

The head of an asylum seekers' organisation said he had last spoken to migrants on board the smaller boat, an inflatable, by satellite phone on 26 March before the line went dead.

"I have meanwhile had no contact with the larger boat, but family members of those on board have called us from Canada, Sweden and Switzerland to tell us they left," said Father Mose Zerai.

The number reportedly on board the inflatable matches the 68 corpses pulled out of the Mediterranean last week and taken to Tripoli, according to Catholic church workers in the Libyan capital. But Zerai said he suspected the bodies, which were found by fishermen, were victims of a different sinking.

"The inflatable with 68 on board was already 60 miles from the Libyan coast when I spoke to them and that seems too far out for Libyan fishermen to be operating," he said.

After a day's delay due to rough seas, three large passenger ferries docked at Lampedusa on Sunday to take 3,000 Tunisian migrants to makeshift camps on the Italian mainland after the Italian prime minister, Silvio Berlusconi, promised on Friday to solve the growing humanitarian crisis on the island.

A caravan at the port was set on fire on Saturday during a demonstration by Tunisians fearing they would be repatriated. Boarding one ferry on Sunday, migrants were handed a towel, soap and deodorant wipes.

Berlusconi said that only 2,500 migrants, part of what he has called a "human tsunami" that has hit Italy, would be left on the island by Sunday evening.

The row over what to do with the 22,000 North Africans, mainly Tunisians, who have landed in Italy this year has now drawn in Italy, France, Tunisia and the EU. Hundreds of migrants have been making for the French border, including 250 who fled on Saturday from a camp at Manduria in Puglia, despite patrols by mounted police, after breaking down a fence while shouting "freedom, freedom".

French police have been rounding up 40 Tunisians a day and returning them across the border into Italy, drawing criticism from the EU as well as the Italian government, which has claimed that once in Europe, the Tunisians are free to circulate. Italy has hinted the migrants could be given temporary documents to help them get past the French border and off Italian soil.

Berlusconi and the French president, Nicolas Sarkozy, discussed joint solutions on Sunday, although plans for mass deportations have run aground due to the refusal of the Tunisian government to take back the migrants.

Berlusconi, under pressure from his all-powerful ally, the Northern League, to expel the migrants, will visit Tunisia on Monday. He is likely to be offering an aid package as an incentive, after a similar mission by two Italian ministers failed to produce results.

But he suggested that Italy could absorb many of the migrants, telling a political rally on Sunday that if Italy's 9,000 local councils each found a job for one Tunisian the problem of the mass landings would be half solved.

"We must remember we were once a country of migrants," Berlusconi said. "We must show understanding and hospitality, because this is a civilised and Catholic country."