A large navy compound in the US capital was on lockdown today amid reports of an "active shooter", but officials later said there was no evidence of a gunman.
Police responded to reports of shots being fired at the Washington Navy Yard - the site of a bloody gun rampage in 2013 - at 7.40am local time.
Officers flooded the area, shutting down more than eight blocks of nearby roads, and launching a building by building search of the sprawling site.
About two hours after the security alert was triggered, officials said there was no evidence of a shooter and no injuries.
Up to 80 employees had taken cover behind "a number of big doors" in a conference room as the incident unfolded, while others sheltered in an office.
Lieutenant commander Scott Williams, 39, told CNN that he saw people running and shouting to "stay away from the cafeteria."
The 41-acre military facility was rocked by a mass shooting in 2013 in which 12 people were killed.
Aaron Alexis, a 34-year-old government technology contractor at the Navy Yard, opened fire on September 16, 2013.
A caller reportedly told authorities today that shots were heard in Building 197, the same one that was the scene of the 2013 killings.
Former sailor Alexis was shot to death after an hour-long exchange with police.
The FBI said Alexis believed electromagnetic waves had been controlling him for months before the rampage.
