WASHINGTON - President-elect Joe Biden was formally recognised as the next president of the United States on Thursday (Jan 7) by a Congress delayed but undeterred by the pro-Trump mob that had earlier occupied the Capitol in a bid to overturn his electoral victory.

The early-morning vote came hours after a mob of pro-Trump protesters stormed the Capitol building, forcing lawmakers to flee to safety and suspend discussions on states' Electoral College votes for the Nov 3 presidential election.

Outgoing President Donald Trump, blamed by many for inciting the mob with his repeated false claims that the election had been stolen from him, promised an orderly transition.

"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 Jan 20," Mr Trump said in a statement on Twitter issued through an aide, after his account was briefly suspended.

Congress, led by Vice-President Mike Pence, certified Mr Biden's victory in an early-morning vote, after lawmakers voted down objections to the Electoral College votes certified by the states, raised by dozens of Republicans loyal to Mr Trump.

Lawmakers had been earlier forced to suspend the proceedings after Trump supporters successfully breached the Capitol.

Smashing windows to enter the building, the supporters fought with Capitol police once inside, brandishing Trump banners and confederacy flags, and cheering from the balconies of the Capitol.

One woman was fatally shot by a police officer, and later died in hospital.

As tear gas was deployed in the Capitol Rotunda, members of Congress were told to put on the gas masks under their seats.

For several hours, the mob wandered through the halls of Congress, posing for selfies in the Senate and House chamber amid scattered papers and overturned desks before they were eventually dispersed by police.

One man was photographed with his feet up on House Speaker Nancy Pelosi's desk. Others emerged from the Capitol showing off items they had stolen from her office.

Police later said that four people died on the Capitol grounds on Wednesday and 52 people had been arrested.

Mr Biden and lawmakers condemned the violence. "In this hour, our democracy is under unprecedented assault, unlike anything we have seen in modern times. An assault on the citadel of liberty, the Capitol itself," he said from Wilmington, Delaware.

Mr Pence, presiding over the Senate as it resumed its debate, said: "To those who wreaked havoc in our Capitol today: You did not win. Violence never wins.".

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

Others blamed Mr Trump for inciting the violence. At a rally earlier in the day, he had urged his supporters to march on the Capitol to "cheer on" Congress and "show strength", promising he would be there alongside them. He was not.

It was clear in the aftermath that Mr Trump had lost some support from allies in Congress.

Republicans initially planned to object to the Electoral College votes from several swing states that Mr Biden won. But after Congress reconvened, several Republican senators said they had changed their minds and, in the end, only Arizona and Pennsylvania were challenged.

In a show of disapproval, the Senate chose not to debate before voting 92-7 to reject the Pennsylvania challenge, although the House debated the full two hours before rejecting the challenge 282-138.

Republican senators also effectively blocked members of the House of Representatives from objecting to results from Georgia, Michigan and Nevada by refusing to join their challenges.

Before proceedings were disrupted, key Republican establishment figures had signalled their rejection of Mr Trump's attempts to overturn the election results.

Mr Pence, who had been publicly pressured by Mr Trump to overturn states' votes, told Congress in a letter that the Constitution did not give him the power to do so.

Mr McConnell rebuked his colleagues as he explained why he would not vote in favour of the option, saying: "If this election were overturned by mere allegations from the losing side, our democracy would enter a death spiral."

Several officials resigned in the wake of Wednesday's events, including Deputy National Security Adviser Matt Pottinger, the First Lady's chief of staff Stephanie Grisham, and special envoy to Northern Ireland Mick Mulvaney.

Several House Democrats said they were discussing drawing up articles of impeachment.

Media outlets reported that some senior administration officials and Republican officials were discussing invoking the 25th Amendment, under which Mr Trump could be removed from office before his term expires on Jan 20.