Joe Biden said Trump had caused one of the "darkest days" in US history.
President-elect Joe Biden launched a blistering attack on Donald Trump on Thursday and the top two Democrats in Congress called for his immediate removal from office over the storming of the US Capitol by his supporters.
Transportation Secretary Elaine Chao became the first member of the cabinet, meanwhile, to step down in protest of Wednesday's shocking attack on the halls of Congress.
Biden, at an event introducing his nominee for attorney general, declined to address the mounting demands for Trump's removal but accused the outgoing Republican leader of an "all-out assault on the institutions of our democracy."
"Yesterday, in my view, was one of the darkest days in the history of our nation," said the 78-year-old Democrat, who is to be sworn in as the 46th US president on January 20.
"They weren't protesters," he said of the Trump supporters who attacked the Capitol while a joint session of Congress was certifying Biden's November 3 election victory. "They were a riotous mob, insurrectionists, domestic terrorists."
"I wish we could say we couldn't see it coming but that isn't true," Biden said. "We could see it coming."
"The past four years, we've had a president who's made his contempt for our democracy, our Constitution, the rule of law clear in everything he has done," he said.
Biden's remarks came as House Speaker Nancy Pelosi and Senate minority leader Chuck Schumer urged Vice President Mike Pence to invoke the 25th Amendment, which allows a majority of the cabinet to remove a president deemed unable to discharge his duties.
"This is an emergency of the highest magnitude," Pelosi said, describing Trump as a "very dangerous person."
"By inciting sedition, as he did yesterday, he must be removed from office," she said. "While it's only 13 days left, any day can be a horror show for America.
"If the vice president and the cabinet do not act, the Congress may be prepared to move forward with impeachment," Pelosi said.
Schumer said Trump "should not hold office one day longer."
"What happened at the US Capitol yesterday was an insurrection against the United States, incited by the president," he said.