All clear ... Washington Navy Yard was put into lockdown amid reports a gunman was on the loose. Picture: AP/Pablo Martinez Monsivais Source: AP

An official briefed on the operation said no one has been arrested, no one was injured and no weapons have been found after a report of gunfire.

The official, who spoke on condition of anonymity because they were not authorised to release the information publicly, said authorities received an alert about a potential shooter on Thursday morning.

That news triggered a large response in keeping with protocols established after a gunman killed 12 workers in a 2013 massacre at the same military facility.

Lockdown ... Police vehicles are seen near the Washington Navy Yard in Washington. Picture: AP/Susan Walsh Source: AP

Traffic jam ... A large police presence gathers in Southeast Washington. Picture: AP/Andrew Harnik Source: AP

Navy security saw surveillance video of two people jumping the fence in the vicinity of the building a couple of minutes before the first report of gunfire, a federal official had said earlier.

Security found no one inside the building, the official said.

A heavy police and fire department presence began blocks away from the Navy Yard, with roads blocked and a helicopter hovering overhead.

Gates to the Navy Yard were closed, and all people were being advised to shelter in place, said Chatney Auger, spokeswoman for Naval District Washington.

Thousands would be at the base at the time of the reports, Navy public affairs officer Chris Johnson told reporters outside the facility.

Authorities stepped up security outside the White House, closing the pedestrian mall that runs along Pennsylvania Avenue and the adjoining Lafayette Square.

Reports shots fired ... An official said shots had been reported in a building on the Washington Navy Yard campus. Picture: AP/Andrew Harnik Source: AP

In September 2013, military contractor Aaron Alexis killed 12 civilian workers at the Navy Yard’s Building 197 before he was fatally shot by police.

The building has since been renamed the Humphreys Building. It reopened this year.

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

Navy Yard has dark history ... Soldiers guard at the Navy Barracks in Washington. Picture: AP/Jacquelyn Martin Source: AP

Little information ... Members of the media gather on the corner of M St. and 4th Street in Southeast Washington. Picture: AP/Andrew Harnik Source: AP

When facilities specialist Chris Robertson heard an alarm and loudspeaker instructions about 7.30am, he said his first thought was: “Here we go again.”

He said his supervisor called at 7.33am and told him and his two co-workers to leave. He also said he hadn’t noticed anything unusual Thursday morning — everything was normal.

The incident comes with the United States on heightened alert ahead of the July 4 national holiday.

The FBI, Department of Homeland Security and National Counterterrorism Centre have warned the public of an increased risk of attack during Independence Day weekend.