A violent mob loyal to Donald Trump stormed the US Capitol and forced legislators into hiding, in a stunning attempt to overturn America’s presidential election, undercut the nation’s democracy and keep Joe Biden from replacing Mr Trump in the White House.

The nation’s elected representatives scrambled to crouch under desks and don gas masks, while police tried to barricade the building, one of the most jarring scenes to unfold in a seat of American political power.

A woman was shot and killed inside the Capitol, and Washington’s mayor instituted an evening curfew in an attempt to contain the violence. Police said three other people died from medical emergencies.

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.

On Thursday morning, Mr Trump pledged there will be an orderly transition after Congress formally validated Mr Biden’s victory, but the support Mr Trump 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.

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 dropped 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.