A congressional hearing into the US Capitol attack by Donald Trump's supporters trying to overturn his 2020 election defeat has presented testimony showing that close allies, even his daughter, rejected his false claims of election fraud.

The House of Representatives select committee investigating the 6 January 2021 assault also showed graphic footage of thousands of rioters attacking police and smashing their way into the Capitol during the first of its six hearings intended to show that Mr Trump tried to subvert the US Constitution and unlawfully hold onto power.

The hearing presented video of testimony or public statements from key Trump administration figures including his daughter Ivanka Trump and her husband Jared Kushner, his vice president Mike Pence and his chief of staff, Attorney General William Barr and General Mark Milley.

It featured a clip of Mr Trump's incendiary speech before the riot in which he repeated his false claims of election fraud and directed his supporters' anger at Mr Pence, who was at the Capitol overseeing the congressional certification of Joe Biden's win.

"Aware of the rioters' chants, to 'Hang Mike Pence,' the president responded with this sentiment: 'Well, maybe our supporters have the right idea," said Representative Liz Cheney, one of the two Republicans on the nine-member panel and its vice chair.

Mr Barr in video testimony called the election fraud claims "bullsh*t," an argument that convinced Mr Trump's daughter.

"I respect Attorney General Barr. So I accepted what he was saying," Ms Trump said in videotaped testimony.

Democratic US Representative Bennie Thompson, the committee's chairman, said Mr Trump was at the centre of a conspiracy to thwart US democracy.

"January 6 was the culmination of an attempted coup, a brazen attempt, as one writer put it shortly after January 6, to overthrow the government," Mr Thompson said "... The violence was no accident. It was Trump's last stand."

Since leaving office last year, Mr Trump has kept up his false claims that 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," Mr Barr, who resigned before Mr Trump left office, said in the video.

Mr Trump, publicly flirting with another White House run in 2024, issued a statement before the hearing calling the committee "political thugs".

Mr Kushner was shown on video dismissing threats by members of Mr Trump's Cabinet to resign after the riot, saying he considered their concerns as "whining."

The hearing also featured two witnesses who testified in person, US Capitol police officer Caroline Edwards, who sustained a brain injury in the attack, and Nick Quested, a filmmaker who captured footage of the far-right Proud Boys group, accused of helping to plan the attack.

Ms Edwards described insults hurled by rioters at her during the melee but said she was proud of fighting them off even after being injured.

"I was slipping in people's blood," Ms Edwards said. "It was carnage. It was chaos."

"What I saw was just a war scene," she added.