Officers engaged the suspect, she added, but he did not respond to verbal commands. One Capitol Police officer and a suspect have died. All three were transported to the hospital, Pittman said. She did not provide additional details, saying next of kin have yet to be notified.

Two law enforcement officials tell The Associated Press that the driver who rammed a vehicle into two police officers outside the U.S. Capitol has died after being shot by authorities. "The process of lowering the flags may take longer than usual because of the Capitol's current lockdown status", said Drew Hammill, Pelosi's deputy chief of staff.

Suspected rioters were seen scaling the Capitol walls, breaking windows, walking onto the Senate and House floor and attacking police officers.

Law enforcement officials confirmed that after hitting the two officers, the driver jumped out of the auto with a knife and was shot by Capitol police. Videos from the scene showed what appeared to be two people on stretchers being loaded into ambulances.

The U.S. Capitol remained on lockdown Friday afternoon after a vehicle rammed a barricade outside the Senate, though the building was largely empty due to a two-week recess. "If you are outside, seek cover", the advisory stated.

Friday's crash and shooting happened at a checkpoint near the U.S. Capitol as Congress is on recess.

The crash occurred about 91 metres from the entrance of the building on the Senate side of the Capitol.

The Washington Metropolitan Police Department, along with assistance from the FBI's Washington Field Office, will take over the investigation into Friday's attack.

The incident comes as the Washington region remains on edge almost three months after a mob of armed insurrectionists stormed the Capitol as Congress was voting to certify Joe Biden's presidential win.

The D.C. National Guard said it deployed a quick reaction force, comprising National Guard soldiers and airmen, to the Capitol complex to support the U.S. Capitol Police. The US Attorney General is also aware of the incident and is being updated, according to CBS News.

The incident came amid tightened security in Washington after the January 6 insurrection by supporters of then-president Donald Trump. An "inner perimeter fence" around the Capitol building is still in place. The crash occurred at an access checkpoint to the Capitol.

NPR congressional correspondent Claudia Grisales reports that there has been considerable concern among lawmakers from both parties about the prospect of making the fencing permanent.

NPR Deputy Washington Editor Krishnadev Calamur contributed reporting.