WASHINGTON - Angry supporters of President Donald Trump stormed the U.S. Capitol on Wednesday in a chaotic protest aimed at thwarting a peaceful transfer of power, forcing lawmakers to be rushed from the building and interrupting challenges to Joe Biden's Electoral College victory.

Trump issued a restrained call for peace well after the melee was underway but did not urge supporters to disperse. Earlier he had egged them on to march to Capitol Hill. The Pentagon said about 1,100 District of Columbia National Guard members were being mobilized to help support law enforcement at the Capitol.

Wednesday's ordinarily mundane procedure of Congress certifying a new president was always going to be extraordinary, with Republican supporters of Trump vowing to protest results of an election that they have baselessly insisted was reversed by fraud. But even the unusual deliberations, which included the Republican vice-president and Senate majority leader defying Trump's demands, were quickly overtaken.

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Protesters

Trump supporters try to break through a police barrier, Wednesday, Jan. 6, 2021, at the Capitol in Washington. As Congress prepares to affirm President-elect Joe Biden's victory, thousands of people have gathered to show their support for President Donald Trump and his claims of election fraud. (AP Photo/Julio Cortez)

Trump supporters at congress

Trump supporters try to break through a police barrier, Wednesday, Jan. 6, 2021, at the Capitol in Washington. As Congress prepares to affirm President-elect Joe Biden's victory, thousands of people have gathered to show their support for President Donald Trump and his claims of election fraud. (AP Photo/Julio Cortez)

Trump supporters

Police hold off Trump supporters who tried to break through a police barrier, Wednesday, Jan. 6, 2021, at the Capitol in Washington. (AP Photo/Julio Cortez)

Pelosi and Pence

Speaker of the House Nancy Pelosi, D-Calif., and Vice President Mike Pence officiate as a joint session of the House and Senate convenes to confirm the Electoral College votes cast in November's election, at the Capitol in Washington, Wednesday, Jan. 6, 2021. (Erin Schaff/The New York Times via AP, Pool)

Congress

House Speaker Nancy Pelosi administers the oath of office to members of the 117th Congress at the U.S. Capitol in Washington, Sunday, Jan. 3, 2021. (Erin Scott/Pool via AP)

In a raucous, out-of-control scene, protesters fought past police and breached the building, shouting and waving Trump and American flags as they marched through the halls. One person was reported shot at the Capitol, according to a person familiar with the situation. That person's condition was unknown.

The protesters abruptly interrupted the congressional proceedings in an eerie scene that featured official warnings directing people to duck under their seats for cover and put on gas masks after tear gas was used in the Capitol Rotunda.

With the crowds showing no signs of abating, Trump tweeted, “Please support our Capitol Police and Law Enforcement. They are truly on the side of our Country. Stay peaceful!” Earlier, at his rally, he had urged supporters to march to the Capitol.

Senators were being evacuated. Some House lawmakers tweeted they were sheltering in place in their offices.

Demonstrators fought with Capitol Police and then forced their way into the building, not long after a huge rally near the White House during which Trump egged them on to march to Capitol Hill.

Lawmakers had convened for an extraordinary joint session to confirm the Electoral College results.

Though fellow Republicans were behind the challenge to Biden's 306-232 Electoral College victory, Senate Majority Leader Mitch McConnell sought to lower tensions and argued against it. He warned the country “cannot keep drifting apart into two separate tribes” with “separate facts.”

McConnell declared, “The voters, the courts and the states all have spoken.”

But other Republicans, including House GOP leaders among Trump's allies were acting out the pleas of supporters at his huge Wednesday rally up Pennsylvania Avenue outside the White House to “fight for Trump.”

“We have to fix this,” said Rep. Steve Scalise of Louisiana, the GOP whip.

The last-gasp effort is all but certain to fail, defeated by bipartisan majorities in Congress prepared to accept the November results. Biden i s to be inaugurated Jan. 20.

Still, Trump vowed to he would “never concede” and urged the massive crowd to march to the Capitol where hundreds had already gathered under tight security.

“We will never give up,” Trump told his noontime rally.

Vice-President Mike Pence was closely watched as he stepped onto the dais to preside over the joint session in the House chamber.

Pence has a largely ceremonial role, opening the sealed envelopes from the states after they are carried in mahogany boxes used for the occasion, and reading the results aloud. But he was under growing pressure from Trump to overturn the will of the voters and tip the results in the president's favour, despite having no legal power to affect the outcome.

“Do it Mike, this is a time for extreme courage!” Trump tweeted Wednesday.

But Pence, in a statement shortly before presiding, defied Trump, saying he could not claim “unilateral authority” to reject the electoral votes that make Biden president.

Despite Trump's repeated claims of voter fraud, election officials and his own former attorney general have said there were no problems on a scale that would change the outcome. All the states have certified their results as fair and accurate, by Republican and Democratic officials alike.

Arizona was the first of several states facing objections from the Republicans as Congress took an alphabetical reading of the election results. Then the chaos erupted.

Associated Press writers Andrew Taylor, Jill Colvin and Kevin Freking in Washington and Bill Barrow in Atlanta contributed to this report.