'All clear' after lockdown at Washington Navy Yard

Over two tense hours after a lockdown on Thursday morning, police gave the 'all clear' at the Washington Navy Yard facility where 12 people were killed in a 2013 shooting.

Around 8 a.m., the US Navy tweeted that the facility was under lockdown, forcing workers to hold-in-place and filled the Southeast neighbourhood of the American capital with police and ambulance vehicles. Bystanders tweeted photos of the scene.

In a preventative measure, officials also closed Pennsylvania Avenue in front of the White House.

A law enforcement official cited by CNN said the move was a standard security precaution in light of potential navy yard incidents under investigation.

But around 10.15 a.m., the capital police said in a statement that the search of the Navy Yard was completed, and that no evidence of shooting or injured personnel was found, CNN reported.

Police said a call was placed from inside a Navy Yard building reporting possible gun shot sounds, which is what prompted the lockdown and investigation. No additional details were immediately available.

Police searched building 197, the same building where the 2013 shooting took place, CNN reported citing a police source who also said the original 911 call reported a shooting on the second floor.

Navy Commander Scott Williams, who was at the Navy Yard on Thursday morning and during the attack two years ago, told CNN that the scene unfolding around the complex was "pretty much a mirror image of 2013".

A defence official cited by CNN said the Pentagon has not raised its security posture at the Pentagon complex in reaction to the situation at Navy Yard, but were keeping a close eye on what is going on.