There was no evidence of a shooter at the Washington Navy Yard on Thursday morning, a Washington police department spokeswoman said two hours after initial reports emerged.
The spokeswoman said the police investigation was concluded and subsequent inquiries would be done by Navy authorities.
Earlier, the Washington Navy Yard, a key Navy site in the US capital went on lockdown on Thursday after reports of shots fired in the same building where a gunman killed 12 workers in a rampage two years ago, but officials said those reports were unconfirmed, with no evidence of a shooting and no weapons found.
No arrests had been made, no weapons were discovered, and no injuries were reported at the Washington Navy Yard, an administrative center for the US Navy, said the officials, who all had been briefed on the situation or had knowledge of it, but spoke on condition of anonymity because they weren't authorized to release details.
Authorities received an alert about a potential shooter, which triggered a large response in keeping with protocols established after the 2013 massacre, one of the officials said.
Navy security saw surveillance video of two people jumping the fence in the vicinity of the building in southeast Washington a couple of minutes before the first report of gunfire, another official. Security found no one inside the building, the official said.
A heavy police and fire department presence began blocks away from the Navy Yard, which is located less than 2 miles (3 kilometers) from the Capitol, with roads blocked and a helicopter hovering overhead. The FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives were on the scene.
Gates to the Navy Yard were closed, and all people were 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.
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.
When facilities specialist Chris Robertson heard an alarm and loudspeaker instructions about 7:30 a.m., he said his first thought was: "Here we go again."
He said his supervisor called at 7:33 a.m. and told him and his two co-workers to leave. He also said he hadn't noticed anything unusual Thursday morning - everything was normal.