Updated 9.50pm -  A man who drew a gun at the US Congress visitors' centre was shot and wounded by  police officers this evening. A woman was slightly injured by shrapnel. 

A U.S. government official told Reuters that initial reports were that a suspect walked into the visitors center and was stopped at a metal detector. He drew a gun and was immediately shot and injured by officers. Several shots were heard. 

There is no reason to believe that this was anything other than a criminal act

In a statement later, the Congress police chief said the police had had previous contact with the gunman.

"There is no reason to believe that this was anything other than a criminal act," he said.

Congress is in recess, with few lawmakers in Washington but the shooting happened just a few hours after a drill for an active shooter took place at the Capitol, creating further confusion.

The Congress building was put on lockdown until police confirmed there were no other suspects.

Cathryn Leff, a licensed therapist, tweeted that she was at the visitor's center when she heard gunshots while going through a security check point.

"That moment when it goes down . Everyone is screaming & running and you can't see where the #ShotsFired are from," tweeted Leff(@Cathrynlefflmft)

In a separate incident, the White House was also briefly put on lockdown after a man tried to climb a fence on the North Lawn. The Secret Service cleared tourists from an area surrounding the White House after the incident, but activities quickly went back to normal.