President-elect Joe Biden on Wednesday denounced the storming of the US Capitol as an "insurrection" and demanded President Donald Trump go on television to call an end to the violent "siege."

"At this hour, our democracy is under unprecedented assault," the veteran Democrat said in Wilmington, after hundreds of Trump supporters protesting his election defeat swarmed the Capitol building and put the nation's lawmakers at risk.

"I call on President Trump to go on national television now to... demand an end to this siege," Biden said. "To storm the Capitol, to smash windows, to occupy offices, the floor of the United States Senate... threatening the safety of duly elected officials? It's not a protest, it's insurrection."