Washington D.C. Mayor Muriel Bowser announced the extension of a public emergency in the American capital to 15 days imposed in the wake of the violent Capitol protests, until the day after President-elect Joe Biden's inauguration on January 20.

The mayor's latest order followed a citywide curfew from Wednesday night to Thursday morning in response to the Capitol chaos, reports Xinhua news agency.

"Today, First Amendment protests turned violent. Many persons came to the District armed and for the purpose of engaging in violence and destruction and have engaged in violence and destruction," Bowser said in a statement on Wednesday night.

"They have fired chemical irritants, bricks, bottles, and guns. They have breached the security of the Capitol and their destructive and riotous behaviour has the potential to spread beyond the Capitol.

"Their motivation is ongoing," she said.

Accusing President Donald Trump of continuing to "fan rage and violence" by contending that the presidential election was invalid, Bowser said: "Persons are dissatisfied with judicial rulings and the findings of State Boards of Elections, and some persons can be expected to continue their violent protests through the inauguration."

On Wednesday afternoon, Trump supporters pushed through barriers at the Capitol building, interrupting the certification of the 2020 electoral votes, and forcing an immediate lockdown and evacuation.

Confrontations between law enforcement officers and protesters have caused injuries from both sides.

At least four people have died around the Capitol area, the police said, adding that 52 people were arrested and 14 police officers sustained injuries.