James Comer, the Oversight Committee chairman, said there was "a mountain of evidence" showing he "abused his public office for his family's financial gain".

"This is a tale as old as time," added another Republican, Jim Jordan.

"Politician takes action that makes money for his family and then he tries to conceal it."

Despite the claims, nothing has proven that Mr Biden abused his position during his eight years as vice president.

The White House has said the impeachment investigation is baseless and politically motivated ahead of next year's likely election showdown with Donald Trump.

A forensic accountant, a former Justice Department official and two law professors appeared at Thursday's session - but nobody with direct knowledge of the allegations.

Professor Jonathan Turley, an impeachment expert called by the Republicans, said the threshold for an inquiry had been passed but there was not enough to impeach.

"I do not believe that the current evidence would support articles of impeachment," Professor Turley said.

Forensic accountant Bruce Dubinsky backed up that assessment.

Another law professor and Democrat witness, Michael Gerhardt, said the evidence wasn't even sufficient for an inquiry.

"A fishing expedition is not a legitimate purpose," he told the hearing.

Republicans claim Mr Biden and his family profited from policies he pursued between 2009 to 2017 and that son Hunter took advantage of his father's name.

"Hunter Biden cashed in by arranging access to Joe Biden, the family brand," Mr Comer told the hearing.

Central to the probe are allegations Joe Biden pressured Ukraine to fire a top prosecutor to stop an investigation into Burisma, an energy firm his son was on the board of.

However, multiple foreign and US officials have said he was only pursuing official policy to fight corruption in pre-war Ukraine.

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It is also claimed the Justice Department interfered with a tax investigation into Hunter Biden - who is set to plead not guilty to a gun charge next month and has struggled with drugs in the past.

Ahead of the hearing, Republicans released documents detailing money transfers from a Chinese businessman to Hunter Biden in 2019 - in which he put his father's address on the form.

Republicans claimed it showed a definite link to the president.

A lawyer for Hunter Biden said the money was a loan and that he had put down his father's address because it was on his driving licence and his only permanent residence at the time.

"Once again Rep Comer peddles lies to support a premise - some wrongdoing by Hunter Biden or his family - that evaporates in thin air the moment facts come out," said lawyer Abbe Lowell.

'No smoking gun'

"If Republicans had a smoking gun or even a dripping water pistol they would be presenting it today. But they've got nothing," said Jamie Raskin, the hearing's top Democrat.

It's unclear if Republicans, who have a slim majority in the House of Representatives, would have enough votes at the end of the inquiry to move forward with the impeachment process.

Even if the vote did go their way, it's extremely unlikely the Senate - where Democrats hold a majority - would vote to remove Mr Biden from power.

Donald Trump was impeached twice during his presidency - one of them for allegedly allegedly pressuring Ukraine to investigate Biden ahead of the 2020 election.

He was acquitted both times by the Senate.

The impeachment hearing comes as House Republicans face off against Democrats over government funding for the fiscal year starting on 1 October.

Large parts of the government will shut down if they cannot agree.

Democrat Jamie Raskin scolded the panel: "We're 62 hours away from shutting down the government of the United States of America and Republicans are launching an impeachment drive, based on a long debunked and discredited lie."