Republicans and Democrats locked arms as a shaken US Congress on Thursday morning formally certified Joe Biden’s election victory, hours after hundreds of Donald Trump’s supporters stormed the Capitol in a harrowing assault on American democracy.

Immediately afterwards, the White House released a statement from Trump in which he pledged an “orderly transition” when Biden is sworn into office on January 20, although he repeated his false claim that he won the November election.

“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,” Trump was quoted as saying.

Police said four people died during the chaos — one from gunshot wounds and three from medical emergencies —and 52 people were arrested.

There was no parallel in modern American history as insurgents acting with the President’s encouragement vandalised Speaker Nancy Pelosi’s office, smashing windows, looting art and briefly taking control of the Senate chamber, where they took turns posing for photographs with fists up on the dais where Vice-President Mike Pence had just been presiding.

Outside the building, they erected a gallows, punctured the tires of a police SUV, and left a note on its windshield saying, “PELOSI IS SATAN.”

Biden said on Wednesday that the activity of the rioters “borders on sedition”.

The attack by rebels carrying pro-Trump paraphernalia stopped the electoral counting for several hours and sent lawmakers and Pence fleeing.

But by the time the Senate had reconvened in a reclaimed Capitol, one of America’s most polarising moments yielded an unexpected moment of solidarity that briefly eclipsed partisan division.

Republicans and Democrats denounced the violence and expressed their determination to carry out what they called a constitutionally sacrosanct function. They refused, by resounding bipartisan majorities, to deliver Trump the election reversal he demanded.

Wednesday’s chaos unfolded after Trump addressed thousands of supporters near the White House and told them to march on the Capitol to express their anger at lawmakers. He told supporters to pressure their elected officials to reject the results, urging them “to fight”.

”There is no question that the President formed the mob, the President incited the mob, the President addressed the mob. He lit the flame,” Representative Liz Cheney, the No. 3 House Republican, wrote on Twitter.

The destructive and shocking images at the Capitol of what other Republicans called an “insurrection” filled television screens in the US and around the world, a deep stain on Trump’s presidency and legacy as his tenure nears its end.

In certifying Biden’s win, long-time Trump allies such as Vice-President Mike Pence and Senate Republican leader Mitch McConnell rejected Trump’s pleas for intervention, while the violence at the Capitol spurred several administration officials to quit.

Among them was Mick Mulvaney, a former White House chief of staff who resigned his post as a special envoy to Northern Ireland. “I wouldn’t be surprised to see more of my friends resign over the course of the next 24 to 48 hours,” he said on CNBC.

A source familiar with the situation said there had been discussions among some cabinet members and Trump allies about invoking the 25th Amendment, which would allow a majority of the cabinet to declare Trump unable to perform his duties, making Pence the acting President. A second source doubted the effort would go anywhere, given Trump has less than two weeks left in office.

Democratic Senator Amy Klobuchar said Trump’s cabinet should be ready to act as Trump could stir up more trouble ahead of Biden's inauguration.

“They better be ready to do that if it continues because you cannot have a President basically leading an insurrection against our own country’s government,” she said on CBS.

McConnell, who had long remained silent while Trump sought to overturn the election results, chastised other Republicans who stalled certification. He called the invasion a “failed insurrection”.

“They tried to disrupt our democracy,” he said on the Senate floor. “They failed.”

The assault on the Capitol was the culmination of months of divisive and escalating rhetoric around the November 3 election.