Hunter Biden, 54, son of US President Joe Biden, made a surprise guilty plea to federal tax charges on Thursday, the first day of his scheduled trial.

He was to stand trial in a Los Angeles federal courthouse on criminal charges of failing to pay $1.4 million in taxes while spending heavily on drugs, sex workers and luxury items. He pleaded guilty to all nine counts he faced.

Judge Mark Scarsi said he faces up to 17 years in prison and up to $450,000 in penalties and set sentencing for Dec 16.

Earlier Thursday, Hunter Biden had offered to plead guilty but not admit any wrongdoing, a legal maneuver called an "Alford plea". Prosecutors opposed the move.

His lawyer Abbe Lowell told the judge his client would plead guilty, despite having no prior agreement with prosecutors.

In a statement after the hearing, Hunter Biden said he pleaded guilty to spare his family from having to sit through a trial that would have aired details of a period when he was addicted to drugs.

"For all I have put them through over the years, I can spare them this," he said, adding that he had paid back his taxes.

Lowell told reporters afterward that Hunter Biden might appeal his sentence. Leo Wise, the lead prosecutor in the case, said he was stunned by the plea and took offense when Lowell suggested that the government had subjected Hunter Biden to an unfair prosecution as a result of political pressure, The New York Times reported.

"This idea that he's a victim of this process, it's offensive," Wise said. "We have not exacted a pound of flesh or a drop of blood. We have afforded him the same right as any American."

A plea deal that Hunter Biden's defense had reached with David Weiss, the special counsel in the case, unraveled when it was reviewed by a federal judge in Delaware in July.

US Representative Jason Smith, a Missouri Republican, one of three congressional committees investigating President Biden via an impeachment inquiry, said,"Hunter Biden's decision to plead guilty once again affirms the integrity of the IRS whistleblowers who recommended these exact charges over two years ago before being stonewalled by the Biden-Harris Justice Department," Fox News reported.

Voters will choose on Nov 5 between Vice-President Kamala Harris, a Democrat and Republican former president Donald Trump. President Biden dropped his reelection bid in July under pressure from his fellow Democrats.

The trial could also have shed light on Hunter Biden's work with Ukrainian natural gas company Burisma and other business dealings while his father was vice-president.

He has denied any improper business dealings and the White House said that President Biden has not benefited from his son's business connections.

The White House has said the president has ruled out pardoning his son, but that did not stop Republicans from claiming otherwise.

"Hunter Biden's bait-and-switch stunt is a clear effort to avoid a messy trial that would reveal his father's role in the family's corrupt business dealings," said Representative Andy Biggs of Arizona, Fox News reported.

Agencies contributed to this story.