WASHINGTON • Reports of a shooting at the Navy Yard in Washington yesterday turned out to be a hoax.

But there were tense moments as the yard was put on lockdown amid unconfirmed reports of an active gunman on the military facility, the scene of a deadly shooting two years ago, the US Navy said.

"#USNavy confirms no sign of shooting @NavalDistWash #NavyYard. All personnel ok. Follow-on NCIS investigation ongoing," the United States Navy later posted on Twitter.

The lockdown came amid security jitters as the United States prepares for the July 4 Independence Day holiday, with major festivities planned in the capital.

A Navy officer, who was inside the complex, told CNN that people scrambled for cover after hearing someone shout to get out of the building. But Lieutenant Commander Scott Williams said he heard no shots and that he did not see any signs of a struggle.

"We heard someone scream, get out of the building, stay away from the cafeteria and we saw everyone running for the exits or adjoining offices," he said.

Television images showed people emerging from the complex with their hands in the air, which workers said was part of their standard evacuation drill.

Police cars converged on the scene in south-east Washington, which led to a huge traffic jam forming outside the complex as two helicopters and an aircraft circled above.

A couple of dozen troops in fatigues were seen massing on a nearby soccer field.

Meanwhile, outside the White House, the authorities stepped up security, closing the pedestrian mall that runs along Pennsylvania Avenue as well as the adjoining Lafayette Square.

The Navy Yard was the scene of a September 2013 shooting that saw a lone gunman fatally shoot 12 people before being killed himself in a shoot-out with police.

The complex houses Navy offices and is the headquarters for a number of naval operations.

AGENCE FRANCE-PRESSE