Police work the scene on M Street S.E. in Washington, where a gunman was reported in a military building at the Washington Navy Yard Monday, Sept. 16, 2013. Shots have been fired and employees directed to a shelter. Police and federal agents from multiple law enforcement agencies responded to the scene and streets in the area were closed. (AP Photo/Jacquelyn Martin)

WASHINGTON - Several people were injured in a shooting Monday morning at a building at the Washington Navy Yard, the U.S. Navy said, and authorities searched for an active shooter.

A defence official, who spoke to The Associated Press on condition of anonymity because he was not authorized to speak during an active attack, also said there were at least several injuries.

The Navy said shots were fired around 8:20 a.m. (1220 GMT) at the Naval Sea Systems Command headquarters, where about 3,000 people work.

The number of the victims and their conditions was not immediately known, though the Navy said multiple people had been injured.

Police and federal agents from multiple law enforcement agencies responded to the scene. Ambulances were parked outside, streets in the area were closed and flights at Reagan National Airport were temporarily halted.

A U.S. Park Police helicopter hovered over the building and appeared to drop a basket or a stretcher with a person onto the roof.

Naval Sea Systems Command is the largest of the Navy's five system commands and accounts for a quarter of the Navy's entire budget. It builds, buys and maintains the Navy's ships and submarines and their combat systems.

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Associated Press writer Lolita C. Baldor in Washington contributed to this report.