Updated at 11:45 p.m. ET

Congress reconvened Wednesday night to certify President-elect Joe Biden's Electoral College victory, just hours after the U.S. Capitol was thrust into chaos by supporters of President Trump — an angry mob that breached the complex in an unprecedented violent act at the seat of America's federal government.

Earlier in the day, the president has urged his backers to head to the Capitol.

A woman was shot and killed during the assault, according to Washington, D.C., police. Her identity has not been made public.

A law enforcement official familiar with the investigation told NPR's Carrie Johnson that the alleged shooter of the woman was a senior U.S. Capitol Police officer and that the woman who was killed was unarmed.

D.C. police said three other adults died after suffering from apparent medical emergencies.

The insurrectionists interrupted proceedings in the House and Senate Wednesday afternoon as members of Congress were tallying Biden's win. The counting of the electoral votes is normally a relatively pro forma session.

But for two months, Trump has falsely and continuously claimed the election was stolen from him, and dozens of fellow Republican allies had planned to object to slates of electors from various states they considered contested.

Lawmakers were debating an objection to Arizona's results — a swing state Trump lost narrowly — when the sessions were recessed as the Capitol Police attempted to put the complex on lockdown.

Violent protesters were seen smashing windows and occupying the House and Senate floors and various lawmakers' offices. Police were seen with guns drawn in the House chamber, pointing their firearms at windows that were smashed.

People inside the building were told to shelter in place, and congressional leaders were taken off-site. Members of Congress were told that tear gas was being used in the Capitol Rotunda and that they should get ready to put on masks.

D.C. police said there were approximately 52 arrests as of 9:30 pm. ET, and that 14 police officers were injured.

The city's mayor, Muriel Bowser, said Wednesday night a review will begin immediately to determine how security at the Capitol was compromised.

Trump urges peace but doubles down on election falsehoods

On Twitter, Trump asked people to remain peaceful. He then posted a video on social media, asking the rioters to go home — but not before reiterating his baseless claims about the election being stolen and saying: "You're very special."

Twitter and Facebook acted to remove the video, and Twitter said it locked Trump's account for 12 hours.

His response to the violence came a few hours after he spoke to thousands of supporters outside the White House, in which he repeatedly denied the results of the election, claiming without evidence it was rigged against his campaign.

"This election was stolen from you, from me, from the country," he said in the earlier remarks. He also urged his supporters to head to the Capitol, adding: "You'll never take back our country with weakness."

Federal and local authorities scrambled to send forces to help secure the Capitol after it was overrun by the pro-Trump extremists. Reinforcements were also being deployed from Virginia, Maryland and New Jersey.

Law enforcement eventually gained control of the scene, ushering people out of the Capitol. The House sergeant at arms informed lawmakers and staff after 5 p.m. that the Capitol had been cleared.

Washington, D.C., instituted a 12-hour curfew that went into effect at 6 p.m. ET Wednesday.

"The President bears responsibility"

Many Republicans, who spent the summer castigating the mostly peaceful protests against racial police violence, had previously encouraged demonstrations calling to overturn the democratic election results.

But current and former politicians from both major parties condemned the breach of the Capitol, with Democrats and many Republicans blaming Trump and his allies for inciting the mob through their repeated claims of a stolen election.

The Democrat Biden said of the attack on the Capitol: "It's not protest; it's insurrection." And he urged the president to "go on national television now to fulfill his oath and defend the Constitution and demand an end to this siege."

"History will rightly remember today's violence at the Capitol, incited by a sitting president who has continued to baselessly lie about the outcome of a lawful election, as a moment of great dishonor and shame for our nation," former President Barack Obama said in a statement. "But we'd be kidding ourselves if we treated it as a total surprise. For two months now, a political party and its accompanying media ecosystem has too often been unwilling to tell their followers the truth — that this was not a particularly close election and that President-Elect Biden will be inaugurated on January 20."

Former President George W. Bush, a Republican, said he was "appalled" by the actions of some political leaders since the election and called the "mayhem" at the Capitol "a sickening and heartbreaking sight."