Violent supporters of President Donald Trump have breached the Capitol in Washington, as lawmakers met to confirm President-elect Joe Biden’s poll win.
In dramatic scenes, demonstrators swarmed the building as Congress members were escorted out by police.
Mr Biden said the action should “end now”, and Mr Trump released a video message asking supporters to go home.
The joint session of Congress certifying Mr Biden’s win has been suspended and forced into recess.
There are reports of guns drawn in the building and at least one person shot. A woman was reported to be in a critical condition after receiving a neck injury.
There has been an armed confrontation at the doors of the House of Representatives. Tear gas has also been used.
Members of Congress have been told to evacuate the building or remain where they are. One congresswoman tweeted that she was staying in her office.
Rioters were seen marching through the building chanting “We want Trump” and one was photographed in the Senate president’s chair.
A citywide curfew has been declared from 18:00 to 06:00 (23:00 to 11:00 GMT) by Washington DC’s mayor.
There are also reports of protests at state legislatures in Kansas and Georgia.
Mr Trump has refused to concede the 3 November election, repeatedly alleging fraud without providing any evidence.
On Wednesday, he said again: “We will never give up. We will never concede.”
He has also tried to throw doubt on the integrity of Tuesday’s Senate run-off votes in the southern, traditionally Republican, state of Georgia. Projections by US TV networks suggest the Democrats have won one of the seats and are neck-and-neck for the second seat.
If the Democrats win both they will gain effective control of the Senate – something that will help Mr Biden push forward his agenda after he is inaugurated as president on 20 January.