The US Capitol Police confirmed the shooting on Capitol Hill in a bulletin, and required staff in all Senate Office buildings to immediately shelter in place and stay away from external doors and windows, Xinhua reported.
The pedestrian walkway before the White House was also quickly locked down after the incident was reported.
Later, the Senate Sergeant at Arms announced via its Twitter account that the lockdown of the area has been lifted and people may exit shelter locations and resume normal activities.
The FBI also dispatched units in response to the incident.
According to White House media pool reports, US President Barack Obama was briefed on the reports of gunfires on Capitol Hill, and the White House staff remained in touch with law enforcement authorities.
The shooting occurred around 2:19 p.m., The Washington Post reported.
It was not immediately confirmed if anyone was shot dead or wounded in the incident.