A suspected gunman has been taken into custody after a shooting at the US Capitol Hill Visitor Centre in Washington, nearby where thousands were attending the annual Easter Egg Roll.

US Capitol Police Chief Matthew Verderosa said after the incident that a lone male gunman known to police entered the visitor centre and drew a weapon while standing at the metal detectors inside the building.

Chief Verderosa said a police officer quickly responded and drew his gun and shot the man, who was then treated on scene and transported to hospital for surgery. His condition was unknown.

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It was earlier thought that a police officer was shot and wounded, but reports confirmed that was untrue. A female bystander was in fact injured by shrapnel, the police Chief said.

Chief Verderos assured this was not a terrorist attack but rather a criminal act.

Children are escorted away from Capitol Hill in Washington. Photo: AAP

A lockdown placed on the US Capitol Visitor Centre and the White House in Washington has been lifted.

Police said gunshots were heard in the US Capitol Visitors Centre and workers were told to shelter just before 6am (AEDT).

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.

“There has been an isolated incident at the US Capitol. There is no active threat to the public,” Washington DC police said on Twitter.

The White House, where thousands were attending the annual Easter Egg Roll, was briefly on lockdown, but the order was quickly lifted.

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,” she tweeted.

The Secret Service temporarily cleared tourists from an area surrounding the White House after the incident, but activities quickly went back to normal.

It temporarily closed the north and south fence lines around the White House complex as a “routine precautionary measure” a spokesman said.

That moment when it goes down ..everyone is screaming & running and you can’t see where the #ShotsFired are from pic.twitter.com/ihfc01nmlt

— Cathryn Leff, LMFT (@Cathrynlefflmft) March 28, 2016

#Capitol on lock down pic.twitter.com/HKXQonJ7HB

— Cathryn Leff, LMFT (@Cathrynlefflmft) March 28, 2016

#video #Capitol #ShotsFired pic.twitter.com/mBHNfYtnuo — Cathryn Leff, LMFT (@Cathrynlefflmft) March 28, 2016

There has been an isolated incident at the US Capitol. There is no active threat to the public — DC Police Department (@DCPoliceDept) March 28, 2016

– with AAP/ABC