Trump told thousands of supporters outside the White House that he would not admit losing his election, as parliament was about to certify Biden's victory.

"We will never give up, we will never lose," President Trump said at a rally in the Ellipse Park area near the White House on Jan. 6, about an hour before the nation's meeting.

"We will block the theft," he said, repeating the argument that he had won but the election was "stolen".

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The meeting of the US Congress to certify the election results is only superficial.

US Vice President Mike Pence, who will chair the meeting as Senate chairman, has been under constant pressure from Trump over the past few days.

"If Mike Pence does the right thing, we'll be elected," Trump told a crowd of cheering supporters.

"And if he doesn't, it will be a sad day for the country," Trump added.

In a bicameral session that can last several hours, if at least one senator and one senator oppose the outcome from one state, the bicameral parliament will meet separately to debate for up to two hours.

To reverse the results, both the House and Senate will have to agree to do so.

The House and Senate are scheduled to contest petitions against electoral votes in at least three states, including Arizona, Georgia and Pennsylvania, which are all winning Biden battlefield states.