House Republicans have branded the first day of their impeachment inquiry against Joe Biden a success, saying they justified their case.

But expert witnesses called by Republicans cautioned there was not yet enough proof for impeachment.

House Speaker Kevin McCarthy announced the inquiry over allegations Hunter Biden engaged in improper business dealings that benefited the president.

The White House has called it a “political stunt”.

The formal impeachment inquiry grants lawmakers greater legal authority to investigate possible misconduct, after months of Republican probes failed to unearth any concrete evidence.

At the first hearing in the inquiry, it was Hunter Biden - not the president - who took up most of the Republican's oxygen. Republicans allege he was selling access to his father.

Republican James Comer of Kentucky, chairman of the powerful Oversight Committee, said the panel would examine more than “two dozen pieces of evidence”, including emails and bank records, which he said would reveal Joe Biden's “corruption and abuse of public office”.

“At least 10 times, Joe Biden lied to the American people that he never spoke to his family about their business dealings,” he said. “The American people demand accountability for this culture of corruption.”

Following the hearing, he announced subpoenas that will force Hunter Biden and President Biden's brother, James, to release their personal and business bank records to the committee.

Failure to comply with the order, which Mr. Comer called “the next step in the investigation”, could result in criminal charges.

Mr. Biden has previously said he “never” discussed business with his son.

Republicans on the committee, though, say Hunter Biden's former business partner Devon Archer told them during a closed-door hearing that Mr. Biden had attended at least two dinners with his son's business associates.

But Mr. Archer also testified that he had never heard business discussed during those encounters.

Chairman Comer and his colleagues also detailed a number of foreign payments to members of President Biden's family, including millions of dollars to Hunter Biden - suggesting the family was involved in a “pay to play” scheme.

One former business partner of Mr. Biden had previously told House investigators the president's son was selling the “illusion of access” to his father.

The investigation will focus on whether Mr Biden ever took any action to directly help his family members' businesses, including meeting with their clients or influencing US government policy.

Democrats pushed back, saying there was no proof that Mr Biden had engaged in improper behaviour.

“If Republicans had a smoking gun or even a dripping water pistol they would be presenting it today,” said Representative Jamie Raskin, the top-ranking Democrat on the committee. “But they've got nothing.”

Hunter Biden's attorney, Abbe Lowell, said in a statement on Thursday “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”.

Thursday's contentious hearing did not feature fact witnesses with direct knowledge about the Bidens. Instead, the panel heard from experts on tax law, criminal investigations and constitutional legal theory.

Two of the three conservative analysts called by Republicans to discuss Mr. Biden's alleged wrongdoing told lawmakers they did not believe there was enough evidence to warrant impeachment.

“I am not here today to even suggest that there was corruption, fraud or wrongdoing,” forensic accountant Bruce Dubinsky said. “More information needs to be gathered before I can make such an assessment.”

Meanwhile, law professor Jonathan Turley told the panel: “I do not believe that the current evidence would support articles of impeachment”.

The sole expert witness called by the Democrats, Michael Gerhardt of the University of North Carolina, told lawmakers he had not seen credible proof to warrant the probe.

Calling the inquiry a “sham” and an “embarrassment”, Democratic committee members sought to refocus the hearing on the looming shutdown and propped up a digital clock counting down to the Saturday deadline when the federal government will run out of money unless Congress reaches a budget deal.

“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,” Mr. Raskin said.

The impeachment inquiry is expected to span weeks. It is too early to tell if congressional investigators will seek an impeachment vote in the full House of Representatives after holding hearings.

Separately, Hunter Biden has been criminally charged with three counts of lying when buying a firearm, after a proposed plea deal collapsed this past summer. (BBC)

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