US Congress reconvenes to certify Biden win after mobs invade Capitol

Congress gavelled back into session late Wednesday to resume the process of certifying Joe Biden's presidential election victory, after a mob protesting Donald Trump's defeat violently invaded the US Capitol and plunged Washington into chaos.

"As we reconvene in this chamber, the world will again witness the resilience and strength of our democracy," Vice President Mike Pence said as he reopened the Senate session.

"To those who wreaked havoc in our Capitol today, you did not win. Violence never wins, freedom wins," Pence added. "And this is still the people's house."

The House of Representatives also resumed its session, with Speaker Nancy Pelosi telling lawmakers they will stay "as long as it takes" to finish the certification of Electoral College votes, the final formal step affirming Biden's win.

"We must and we will show to the country, and indeed to the world, that we will not be diverted from our duty, that we will respect our responsibility to the constitution and to the American people."

Both chambers were forced into recess earlier as they were debating the objection by some Republicans to the Electoral Vote count in Arizona, a swing state that voted for Biden.

Lawmakers of both parties reentered their chambers under heavy security escorts hours after the unrest, which saw protesters breach barricades, and push past police into the House and Senate.

Security agents drew weapons inside the House chamber during a dangerous standoff that left lawmakers fearing for their lives.

A number of senators who said they had intended to support the objection reversed course following the violence, including Kelly Loeffler who just Tuesday lost her special election in Georgia in a runoff that led to Democrats gaining control of the chamber.

"When I arrived in Washington this morning I fully intended to object to the certification of electoral votes," she told her colleagues during the debate. 

"However, the events that have transpired today have forced me to reconsider, and I cannot in good conscience object to the certification of these electors."

The Senate's Republican leader, Mitch McConnell, sought to present a united front against the rioters who triggered the Washington mayhem.

"The United States Senate will not be intimidated. We will not be kept out of this chamber by thugs, mobs or threats," said McConnell.

"We're going to finish exactly what we started... and we will certify the winner of the 2020 presidential election."

Democratic leader Chuck Schumer laid responsibility for the chaos directly at the feet of the president.

"This mob was in good part President Trump's doing, incited by his words, his lies. This violence in good part his responsibility, his everlasting shame, Schumer said.

"This will be a stain on our country not so easily washed away, the final, terrible indelible legacy of the 45th president of the United States."

Agencies contributed to this report.