Four people have died after Donald Trump supporters stormed Capitol Hill in Washington DC and clashed with police.
The incident yesterday afternoon forced lawmakers to crouch under desks and don gas marks, while police futilely tried to barricade the building.
A woman was fatally shot in the Capitol building as the mob advanced, according to DC Police Chief Robert Contee. Three others died in “medical emergencies.”
The protesters were apparently driven by the desire to stop the certification of the presidential election in favour of Joe Biden.
This morning, the US Congress certified enough Electoral College votes for Mr Biden to confirm his victory in the presidential race.
With Congress approving Vermont's votes, Mr Biden now has at least the 270 Electoral College votes needed to claim the presidency.
A senior adviser to Donald Trump issued a statement from the outgoing president saying he "totally disagrees" with the election result but vowed there would be an orderly transition to Joe Biden's administration.
Dan Scavino, the White House deputy chief of staff for communications, tweeted: "Even though I totally disagree with the outcome of the election, and the facts bear me out, nevertheless there will be an orderly transition on January 20th.
"I have always said we would continue our fight to ensure that only legal votes were counted. While this represents the end of the greatest first term in presidential history, it's only the beginning of our fight to Make America Great Again!"
The rioters were egged on by Mr Trump, who had spent weeks falsely attacking the integrity of the election and urged his supporters to descend on Washington to protest against Congress's formal approval of Mr Biden's victory.
Some Republican legislators were in the midst of raising objections to the results on his behalf when the proceedings were abruptly halted by the mob.
The protests and the Republican election objections exposed the depths of the divisions that have coursed through the country during Mr Trump's four years in office.
Though the efforts to block Mr Biden from being sworn in on January 20 were sure to fail, the support Mr Trump has received for his efforts to overturn the election results have badly strained the nation's democratic safeguards.
Congress reconvened in the evening, legislators condemning the protests that defaced the Capitol and vowing to finish confirming the electoral college vote for Mr Biden's election, even if it took all night.
Vice president Mike Pence, reopening the Senate, directly addressed the demonstrators, saying: "You did not win."
Republican Senate majority leader Mitch McConnell said the "failed insurrection" underscored legislators' duty to finish the count. Democratic House speaker Nancy Pelosi said Congress would show the world "what America is made of" with the outcome.
The president had given his supporters a boost into action on Wednesday morning at a rally outside the White House, where he urged them to march to the Capitol.
He spent much of the afternoon in his private dining room off the Oval Office watching scenes of the violence on television. At the urging of his staff, he reluctantly issued a pair of tweets and a taped video telling his supporters it was time to "go home in peace" - yet he still said he backed their cause.
Hours later, Twitter for the first time time locked his account, demanded that he remove tweets excusing violence and threatened "permanent suspension".
A sombre president-elect Biden, two weeks away from being inaugurated, said American democracy was "under unprecedented assault", a sentiment echoed by many in Congress, including some Republicans. Former President George W Bush said he watched the events in "disbelief and dismay".
The Capitol building has for centuries been the scene of protests and occasional violence, but Wednesday's events were particularly astounding because they unfolded at least initially with the implicit blessing of the president, and because of the underlying goal of overturning the results of a free and fair presidential election.
Tensions were already running high when legislators gathered early on Wednesday afternoon for the constitutionally mandated counting of the electoral college results, in which Mr Biden defeated Mr Trump, 306-232.
Mr Trump spent the lead-up to the proceedings publicly hectoring Mr Pence, who had a largely ceremonial role, to aid the effort to throw out the results. He tweeted: "Do it Mike, this is a time for extreme courage!"
But Mr Pence, in a statement shortly before presiding, defied Mr Trump, saying he could not claim "unilateral authority" to reject the electoral votes that make Mr Biden president.
In the aftermath, several Republicans announced they would drop their objections to the election, including senator Kelly Loeffler, who lost her bid for re-election on Tuesday.
Earlier, protesters had fought past police and breached the building, shouting and waving Trump and American flags as they marched through the halls, many without masks during the Covid-19 crisis.
Legislators were told to duck under their seats for cover and put on gas masks after tear gas was used in the Capitol Rotunda. Some House members tweeted they were sheltering in place in their offices.
The woman who was killed was part of a crowd breaking down the doors to a barricaded room where armed officers stood on the other side, police said. She was shot in the chest by Capitol police and taken to a hospital where she was pronounced dead.
City police said three other people died from medical emergencies during the long protest on and around the Capitol grounds.
