Hunter Biden, son of U.S. President Joe Biden, and his wife Melissa leave the federal court building, in Los Angeles [Source: Reuters]

Hunter Biden, son of US President Joe Biden, has pleaded guilty to federal tax charges in a surprise move that avoids a potentially embarrassing trial weeks before the US presidential election.

Biden had been set to stand trial in a Los Angeles federal courthouse on criminal charges of failing to pay $US1.4 million ($A2.1 million) in taxes while spending lavishly on drugs, sex workers and luxury items.

Instead, he pleaded guilty on Thursday to all nine counts he faced.

Judge Mark Scarsi told Biden he faces up to 17 years in prison and up to $US450,000 ($A668,000) in penalties. He set sentencing for December 16.

Defendants who plead guilty in criminal cases typically work out an agreement with prosecutors beforehand, hoping to receive a lower sentence in exchange for avoiding trial.

That did not appear to be the case here.

Earlier in the day, Biden had offered to plead guilty to the charges but avoid admitting wrongdoing, an unusual legal manoeuvre opposed by prosecutors.

“It’s not clear to us what they are trying to do,” one prosecutor told the judge.

The guilty plea heads off a weeks-long trial that likely would have aired messy details of Hunter Biden’s life during the election campaign. Voters will choose on November 5 between Vice President Kamala Harris, a Democrat, and Republican former president Donald Trump. Joe Biden dropped his re-election bid in July under pressure from his fellow Democrats.

Hunter Biden, who has been open about his struggles with drug and alcohol addiction, is accused of failing to pay taxes from 2016 to 2019 while spending huge sums “on drugs, escorts and girlfriends, luxury hotels and rental properties, exotic cars, clothing, and other items of a personal nature,” according to an indictment.

The trial could also have shed light on his work with Ukrainian natural gas company Burisma and other business dealings while his father was vice president. The president’s Republican foes have claimed those activities by his son were corrupt.

The indictment says Hunter Biden “earned handsomely” while serving on the boards of Burisma and a Chinese private equity fund.

Hunter Biden has denied any improper business dealings and Republican-led investigations in Congress have not directly implicated his father in any wrongdoing.

He is appealing a guilty verdict in a separate case in Delaware for illegally buying a gun while using drugs.

That conviction means he could face a stiffer sentence for the tax case if convicted, because he would be a repeat offender.