WASHINGTON, Jan 7 ― Hundreds of supporters of President Donald Trump stormed the US Capitol today in a bid to overturn his election defeat, forcing Congress to postpone a session that would have certified President-elect Joe Biden's victory.

With drawn guns and tear gas, police evacuated lawmakers and sought to clear the Capitol Building of the Trump supporters, who surged through the halls of Congress in shocking scenes broadcast across the globe.

One protester occupied the Senate dais and yelled: “Trump won that election.” Protesters overturned barricades and clashed with police as thousands descended on the Capitol grounds.

Police declared the Capitol building secure shortly after 5.30pm (2230 GMT), more than three hours after it was breached.

Video showed the Trump supporters breaking windows and police deploying tear gas inside the building. Washington Metropolitan Police Chief Robert Contee said members of the crowd used chemical irritants to attack police and several had been injured. One civilian died after being shot during the mayhem, local media said. The FBI said it had disarmed two suspected explosive devices.

It was the most damaging attack on the iconic building since the British army burned it in 1814, according to the US Capitol Historical Society.

The chaotic scenes unfolded after Trump, who before the election refused to commit to a peaceful transfer of power if he lost, addressed thousands of protesters, repeating unfounded claims that the election was stolen from him due to widespread fraud and irregularities.

Biden, a Democrat who defeated the Republican president in the November 3 election and is due to take office on January 20, said the activity of the protesters “borders on sedition.”

The former vice president said that for demonstrators to storm the Capitol, smash windows, occupy offices, invade Congress and threaten the safety of duly elected officials: “It's not a protest, it's insurrection.”

He urged Trump to demand “an end to this siege” on national television.

In a video posted to Twitter, Trump repeated his false claims about election fraud but urged the protesters to leave.

“You have to go home now, we have to have peace,” he said, adding: “We love you. You're very special.”

Twitter Inc later restricted users from retweeting Trump's video, and Facebook Inc took it down entirely, citing the risk of violence.

Vice President Mike Pence, who had presided over the joint session of Congress, had already been escorted from the Senate.

Lawmakers had been debating a last-ditch effort by pro-Trump lawmakers to challenge the results, which was unlikely to succeed.

Critics had called the effort by the Republican lawmakers an attack on American democracy and the rule of law and an attempted legislative coup.

The top two Democrats in Congress, House of Representatives Speaker Nancy Pelosi and Senator Chuck Schumer, called on Trump to demand that all the protesters leave the Capitol and its grounds immediately.

Capitol Police told lawmakers in the House chamber to take gas masks from beneath their seats and ordered them to drop to the floor for their safety. Officers drew their guns as someone tried to enter the House chamber.

Police piled furniture against the doors of the House chamber as protesters tried to break them down, Democratic Representative Jason Crow said on MSNBC.

Several hundred House members, staff and press were later evacuated to an undisclosed location.

Election officials of both parties and independent observers have said there was no significant fraud in the November 3 contest, which Biden won by more than 7 million votes in the national popular vote.

Weeks have passed since the states completed certifying that Biden won the election by 306 Electoral College votes to Trump's 232. Trump's extraordinary challenges to Biden's victory have been rejected by courts across the country.

‘We will not take it’

Trump had pressed Pence to throw out election results in states the president narrowly lost, although Pence has no authority to do so.

“Our country has had enough and we will not take it any more,” Trump said at the rally.

The certification in Congress, normally a formality, had been expected to stretch for several hours as some Republican lawmakers mounted an effort to reject some state tallies, starting with Arizona.

Republicans and Democrats, who had been bitterly divided over that effort, both called on the Trump supporters to stand down.

“This is un-American and this has to stop,” said House Republican leader Kevin McCarthy, a Trump ally who supported the Republican effort to challenge the results.

That attempt was unlikely to succeed, as even many Republicans opposed it.

“If this election were overturned by mere allegations from the losing side, our democracy would enter a death spiral,” said Senate Majority Leader Mitch McConnell, who helped give Trump some of his biggest accomplishments.

Washington Mayor Muriel Bowser ordered a citywide curfew starting at 6pm (2300 GMT).

National Guard troops, FBI agents and US Secret Service were deployed to help overwhelmed Capitol police.

The violence unfolded on the same day that Trump's Republicans lost their majority in the Senate as they lost two runoff elections in Georgia.

“We will never give up,” Trump earlier told thousands of cheering supporters on a grassy expanse near the White House called the Ellipse. “We will never concede. It doesn't happen.”

Trump called on Pence to overturn the election results as he presided over the debate in Congress. “If you're not, I'm going to be very disappointed in you,” Trump said.

The US Constitution does not give Pence the power to unilaterally overturn the results of the election, and the vice president said in a statement he could not accept or reject electoral votes unilaterally.

The violence stunned world leaders. “Trump and his supporters must accept the decision of American voters at last and stop trampling on democracy,” German Foreign Minister Heiko Maas said.

Business groups, normally staunch allies of Republicans in Washington, also reacted strongly. The National Association of Manufacturers said Pence should consider invoking a clause in the Constitution that allows a president to be removed from office when he is unable to do his job.

“This is sedition and should be treated as such,” said the group's president, Jay Timmons. ― Reuters