US lawmakers have certified Joe Biden's election victory, hours after Trump supporters stormed the Capitol in an attack that saw four people die.

One woman was shot by police, while three others died as a result of "medical emergencies", officials said.

The mob, which had been encouraged by President Trump, stormed the building in a bid to overturn the election result, suspending a Congress session.

The president-elect blasted the "insurrection".

President Donald Trump later called on them to "go home" while continuing to make false claims of electoral fraud. Twitter and Facebook later froze his accounts.

US Vice-President Mike Pence started the resumed session on Wednesday evening, in which lawmakers are counting and confirming electoral votes, saying it had been a "dark day in the history of the United States Capitol".

Some Republican lawmakers' objections to overturn the result in Arizona and Pennsylvania were rejected. The session confirmed Mr Biden's 306 votes to Mr Trump's 232.

The rampage came as two Democrats won Senate seats in elections in Georgia, which shifted the balance of Congress to their party's effective political control, aiding the passage of Mr Biden's agenda after he is inaugurated on January 20.

Washington DC Mayor Muriel Bowser said the woman shot by police was part of a group of individuals that forced entry into the House room, which was still in session. They were confronted by plainclothes officers, and an officer pulled out a weapon and fired it.

The woman was taken to hospital and proclaimed dead. She has not been officially named, but local media identified her as San Diego-area US Air Force veteran and Trump supporter Ashli Babbit.

Officials said the three other deaths included one woman and two men, but details of how they died have not been made public. At least 14 members of the police were injured during the unrest.

Protesters surged up the Capitol steps at about 14:15 local time (19:15 GMT), shoving past barricades and officers in riot gear to penetrate the building.

The action was targeting the joint session of Congress being held to certify Mr Biden's election victory on 3 November. The invasion sent members of Congress scrambling for cover under their seats as tear gas was fired.

The mob - some of whom wore body armour - used chemical irritants to attack police, according to Washington Metropolitan Police Chief Robert Contee.

They shouted and waved pro-Trump and US flags as they roamed the halls, demanding the results of the presidential election be overturned.

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

Two pipe bombs were recovered, one from the Democratic National Committee offices, not far from the Capitol, and one from the nearby Republican National Committee headquarters.

The occupation of the Capitol lasted more than three hours before the building was secured by law enforcement. But there was little sign the protesters were heeding Mr Trump's call to go home, despite a citywide curfew declared by the city mayor from 18:00 to 06:00.

So far, more than 52 people have been arrested - 47 of them for curfew violations.

There were also protests on Wednesday at state legislatures in Kansas, Georgia, Utah and on the other side of the country in Oregon and the north-western state of Washington.