HOUSE Speaker Nancy Pelosi has said President Donald Trump should immediately be removed from office or Congress may proceed to impeach him.

Pelosi joined those calling on the Cabinet to invoke the 25th Amendment to force Trump from office. It came after a violent mob of Trump supporters stormed the Capitol, forcing the building into lockdown.

Pelosi said at the Capitol: “The President of the United States incited an armed insurrection against America.”

She also warned that he could do further harm to the country: “Any day can be a horror show for America.”

Democrats and some Republicans want Trump removed before his term ends on January 20 with Joe Biden’s inauguration. The 25th Amendment allows for the vice president and a majority of the Cabinet to declare the president unfit for office. The vice president then becomes acting president.

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Republican congressman Adam Kinzinger and top Democrat Chuck Schumer have also called for the 25th Amendment to be invoked.

In another blow to Trump, transportation secretary Elaine Chao said she is resigning, becoming the highest ranking member of the administration to quit after the insurrection at the Capitol.

Chao, who is married to Senate Republican leader Mitch McConnell, said the violent attack on the Capitol “has deeply troubled me in a way that I simply cannot set aside”.

Kinzinger, from Illinois, said: “The president is unfit. And the president is unwell.”

The call was echoed by Chuck Schumer, a senior Democrat. He tweeted: “What happened at the US Capitol yesterday was an insurrection against the United States, incited by President Trump. This president must not hold office one day longer.”

The US Defence Department has formally activated roughly 6200 members of the National Guard from six states to help support the Capitol Police and other law enforcement in Washington in the wake of the deadly riot that rocked the US Capitol.

A defence official said the goal is to have Guard members help secure the US Capitol before the January 20 inauguration of president-elect Joe Biden. The order comes after armed protesters forced Congress to halt the vote to certify the election result.

The vote was later completed after the building was cleared, certifying Joe Biden and Kamala Harris as the next president and vice-president.

Trump was also removed from Twitter and Facebook, with Mark Zuckerberg saying Trump’s “decision to use his platform to condone rather than condemn the actions of his supporters at the Capitol building has rightly disturbed people in the US and around the world.”

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Zuckerberg added: “Over the last several years, we have allowed President Trump to use our platform consistent with our own rules, at times removing content or labelling his posts when they violate our policies.

“We did this because we believe that the public has a right to the broadest possible access to political speech, even controversial speech. But the current context is now fundamentally different, involving use of our platform to incite violent insurrection against a democratically elected government.

“We believe the risks of allowing the president to continue to use our service during this period are simply too great. Therefore, we are extending the block we have placed on his Facebook and Instagram accounts indefinitely and for at least the next two weeks until the peaceful transition of power is complete.”

Twitter said three of Trump’s tweets had to be removed due to “severe violations of our Civic Integrity policy”.

In a statement the company said Trump’s account would be locked for 12 hours, and he would be banned permanently if the tweets were not deleted.