The Jan 6, 2021, riot followed shortly after the then president gave an incendiary speech to thousands of supporters repeating his false claims of a stolen 2020 election and urging them to march on the Capitol and "fight like hell".

Even members of his own administration, including then attorney-general Bill Barr - as seen in video shown by the House of Representatives select committee - rejected Trump's claims of widespread election fraud in his loss to Joe Biden.

The hearing began with Barr's video testimony calling the fraud claims "bulls**t", an argument that had convinced Trump's daughter.

"I respect attorney-general Barr. So I accepted what he was saying," Ivanka Trump said in videotaped testimony.

The panel also showed video testimony from other senior Trump White House officials including then-vice president Mike Pence's chief of staff.

"Jan 6 was the culmination of an attempted coup, a brazen attempt, as one writer put it shortly after Jan 6, to overthrow the government," Democrat Bennie Thompson, the committee's chairman, said in his opening statement.

"The violence was no accident. It was Trump's last stand."

One of the two Republicans on the committee, its vice chairwoman Liz Cheney, noted Trump dismissed the threats that rioters made against Pence as they stormed the Capitol, where Pence was to preside over the congressional certification of the 2020 election results.

"Aware of the rioters' chants, to 'Hang Mike Pence', the president responded with this sentiment: 'Well, maybe our supporters have the right idea," Cheney said.

Since leaving office last year, Trump has kept up his false claims his 2020 election loss was the result of widespread fraud, an assertion that has been rejected by multiple courts, state election officials and members of his own administration.

"We can't live in a world where the incumbent administration stays in power based on its view, unsupported by specific evidence, that there was fraud in the election," said Barr, who resigned before Trump left office.

Close Trump associates who have spoken to the committee include his son Donald Jr, daughter Ivanka and son-in-law Jared Kushner, former acting attorney-general Jeffrey Rosen, former attorney-general Barr and senior aides to former vice president Pence.

Trump, publicly flirting with another White House run in 2024, called the committee in a statement "political thugs".

The hearing will also feature two in-person witnesses - US Capitol police officer Caroline Edwards, who sustained a traumatic brain injury in the attack, and Nick Quested, a filmmaker who captured footage of the far-right Proud Boys group, accused of planning the deadly attack.

Other Capitol Police officers who fought with rioters on Jan 6 were present in the audience for the hearing including Officer Harry Dunn, who wore a T-shirt bearing the word "insurrection", and Officer Michael Fanone, who was beaten and electrocuted during the attack.

A total of six hearings are expected this month as the Democratic-led committee attempts to reverse Republican efforts to downplay or deny the violence of the attack, with five months to go until the November 8 midterm elections that will determine which party controls the House and the Senate for the following two years.

The pro-Trump mob failed to prevent Congress from certifying Biden's victory, attacking police and causing millions of dollars in damage.

Four people died on the day of the attack, one fatally shot by police and the others of natural causes.

More than 100 police officers were injured, and one died the next day. Four officers later died by suicide.

"Those who invaded our Capitol and battled law enforcement for hours were motivated by what President Trump had told them: That the election was stolen and that he was the rightful president," Cheney said.

"President Trump summoned the mob, assembled the mob and lit the flame of this attack."

Biden on Thursday described the attack as "a clear, flagrant violation of the Constitution".

"These guys and women broke the law, tried to turn around the result of an election," he said.

Australian Associated Press