Police in the U.S. Capitol on Wednesday responded with drawn guns and teargas as hundreds of protesters stormed the building and sought to force Congress to undo President Donald Trump's election loss shortly after some of Trump's fellow Republicans launched a last-ditch effort to throw out the results.

Members of the House of Representatives and the Senate were evacuated after pro-Trump protesters marched through the halls of Congress, forcing both chambers to suspend deliberations as they were meeting to certify President-elect Joe Biden's victory in the Nov. 3 election.

One protester occupied the Senate dais and yelled, "Trump won that election." Protesters overturned barricades and clashed with police as thousands descended on the Capitol grounds.

Video showed protesters breaking windows and police deploying teargas inside the building. Local media reported that one person had been shot and video showed a person being wheeled from the building on a stretcher.

Vice President Mike Pence, who had presided over the joint session of Congress, had already been escorted from the Senate.

The chaotic scenes unfolded after Trump, who is due to leave office on Jan. 20, addressed thousands of protesters, repeating false claims that the election was stolen from him due to widespread election fraud and irregularities. Lawmakers had been debating a last-ditch effort by pro-Trump lawmakers to challenge the results, an effort that was unlikely to succeed.

Critics had called the effort by the Republican lawmakers an attack on American democracy and the rule of law and an attempted legislative coup.

The top two Democrats in Congress, House Speaker Nancy Pelosi and Senator Chuck Schumer, called on Trump to demand that all the protesters leave the Capitol and its grounds immediately.

Capitol Police told lawmakers in the House chamber to take gas masks from beneath their seats and prepare to put them on. Officers at the front door of the House chamber had their guns drawn as someone attempted to enter the chamber.

Officers ordered people in the chamber to drop to the floor for their safety. Several hundred House members, staff and press were evacuated to an undisclosed location and were told not to leave.

Election officials of both parties and independent observers have said there was no significant fraud in the Nov. 3 contest, which Biden won by more than 7 million votes in the national popular vote.

Weeks have passed since the states completed certifying that Biden, a Democrat, won the election by 306 Electoral College votes to Trump's 232. Trump's extraordinary challenges to Biden's victory have been rejected by courts across the country.

'WE WILL NOT TAKE IT'

Trump had pressed Pence to throw out election results in states the president narrowly lost, though Pence has no authority to do so.

"Our country has had enough and we will not take it any more," Trump said at the rally.

The certification in Congress, normally a formality, had been expected to stretch for several hours as some Republican lawmakers mounted an effort to reject some state tallies, starting with Arizona.

Republicans and Democrats, who had been bitterly divided over that effort, both called on protesters to stand down.

"This is un-American and this has to stop," said House Republican Leader Kevin McCarthy, a Trump ally who supported the Republican effort to challenge the results.

That attempt was unlikely to succeed, as even many Republicans opposed it.

"If this election were overturned by mere allegations from the losing side, our democracy would enter a death spiral," said Senate Majority Leader Mitch McConnell, who helped give Trump some of his biggest accomplishments.

Schumer called the challenges in Congress by Trump allies "an attempted coup" and said, "The Congress does not determine the outcome of an election. The people do."

Outside the Capitol, members of militia groups and far-right groups, some in body armor, mingled with the crowds.

On Twitter, Trump called on protesters to stay peaceful.

Washington Mayor Muriel Bowser ordered a citywide curfew starting at 6 p.m. (2300 GMT).

Pence rebuffed Trump's demand that he reject state electoral votes on the same day Trump's fellow Republicans were poised to lose their majority in the Senate.

"We will never give up," Trump earlier told thousands of cheering supporters on a grassy expanse near the White House called the Ellipse. "We will never concede. It doesn't happen. You don't concede when there's theft involved."

"Mike Pence, I hope you're going to stand up for the good of our Constitution and the good of our country. And if you're not, I'm going to be very disappointed in you," Trump said.

In a statement, Pence said he shares the concerns about the "integrity" of the election but that is not correct that he should be able to accept or reject electoral votes unilaterally.

The U.S. Constitution does not give Pence the power to unilaterally overturn the results of the election.