Four people died as masses of angry pro-Trump protesters stormed the Capitol on Wednesday, Washington DC police chief Robert Contee said.
One woman was shot by police in the Capitol building, and later died in hospital, Contee said. Contee said the incident would be investigated internally, and offered his condolences to the victim's family.
Another woman and two men died as a result of separate medical emergencies.
Some 52 people were arrested, 4 of them on weapons charges and 47 for violating the nighttime curfew which went into place at 6pm Wednesday.
Contee went on to say that at least 14 police officers were injured in the clashes, two of them seriously.
One of those officers was pulled into the crowd by protesters, where he was attacked and the second suffered significant facial injuries when he was hit by a projectile, he said.
Police officers try to stop protesters as they storm the US Capitol. Photo: Miguel Juarez Lugo/dpa.
Clashes with police
The protests began hours after US President Donald Trump riled up his supporters with baseless allegations of election fraud and encouraged them to march to the Capitol.
Protesters clashed with police and stormed the Capitol, where lawmakers were due to certify president-elect Joe Biden's win in the November election.
Television footage showed protesters inside after breaking in through a window, banging on the doors of the chambers.
The Senate and House of Representatives abruptly called off their sessions, where they had been debating Republican challenges to results in US states that Biden won, as the building went into lockdown.
Trump supporters storm the Capitol building. Photo: Essdras M. Suarez/dpa.
The situation was fraught, with tear gas and some flares being used. There were militias from multiple states and protesters flew Trump and QAnon flags from the steps of the building.
"Obviously this is not what we want to happen but it's what we need to happen now," one supporter said. "Hang the traitors," another said.
Trump was under increasing pressure to denounce the action.
"I am asking for everyone at the US Capitol to remain peaceful. No violence!" he tweeted.
At the earlier rally, Trump told the cheering crows that "we will never concede... You don't concede when there's theft."
Clashes between Donald Trump's supporters and the police. Photo: Essdras M. Suarez/dpa.
Protesters from dozens of states
Protesters descended on the capital from dozens of states across the country to support his claims, shunning face masks despite the raging coronavirus pandemic, while some waved Confederate flags and wore t-shirts that said "nuke the swamp."
"I am from Detroit and I saw the fraud. The fraud is real, the evidence is overwhelming," Ben Cushman of Michigan said.
Trump had goaded supporters to join the demonstration, which included a melange of right-wing groups such as QAnon supporters and militia members.
Washington Mayor Muriel Bowser issued a 6 pm curfew after the protesters breached the Capitol. She had called in National Guard troops and urged residents to avoid confrontations with protesters ready to use violence.
Congress had come together for a joint session to certify the US presidential election. Normally a procedural affair, it had turned into a partisan showdown as Trump allies mounted a last-ditch effort to overturn his loss.
Some Republican lawmakers objected to Congress certifying Biden's victory over Trump in the US state of Arizona, the first of several expected challenges to state results.
The highly unusual move broke up the joint session, a typically routine step in confirming which candidate won the presidential election, and prompted both chambers to withdraw to debate the challenge for two hours.
The challenges are almost certain to be overruled, but could delay the process.
A Donald Trump supporter breaks a window of the US Capitol building. Photo: Carol Guzy/dpa.
Biden won the election
Biden, a Democrat, won both the popular vote and the necessary number of Electoral College votes to be declared the winner of the November presidential election.
A group of Republican senators, led by Josh Hawley and Ted Cruz, as well as dozens of Republicans in the House of Representatives, had vowed to reject Biden's win in several states unless there is an audit of the election results.
The moves have split the Republican party, with Senate Majority Leader Mitch McConnell saying that overruling voters would damage the country forever.
"I will vote to respect the people's decision and defend our system of government as we know it," he told the debate on the Senate floor.
Vice President Mike Pence, whose role is largely ceremonial and involves reading out the vote results, has been thrust into the spotlight as he has come under pressure from Trump to declare him the winner of the election.
But in a letter to Congress ahead of the session, Pence defied the president by saying he could not claim "unilateral authority" to reject the electoral votes of states that Biden won.
Pence's resistance could set up a clash with Trump, who earlier told thousands of supporters that it would be a "sad day for our country" if Pence did not "come through for us."