New York, New York - Donald Trump's unprecedented criminal trial is set for opening statements next week after final jury selection ended Friday, leaving the Republican presidential candidate facing weeks of hostile testimony that will overshadow his White House campaign.

The milestone on Friday in the first criminal trial of a former or sitting US president coincided with a man setting himself on fire outside the Manhattan courthouse.

The self-immolation did not appear to have anything to do with Trump's case. Authorities said the man was in hospital in critical condition and had been carrying pamphlets referring to an unrelated conspiracy theory.

The full jury of 12 New Yorkers and six alternates had just been completed when the incident occurred on the street outside the building where the ex-president and Republican candidate for November sat on the 15th floor.

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Judge Juan Merchan has said that opening statements in Trump's trial would start Monday.

Trump has pleaded not guilty to 34 counts of business fraud as part of a plan to cover up hush money paid to a porn star so that the story would not come out just before the 2016 presidential election, in which he beat Hillary Clinton.

The difficulty of choosing impartial jurors, who must also be able to set aside as much as two months of their time, has been clear throughout the selection process this week.

Two women in the pool of dozens of ordinary New Yorkers being vetted for the final jury slots Friday burst into tears as they answered probing questions from attorneys.

"I'm sorry. I thought I could do this," said one who was quickly released by Merchan. "This is so much more stressful than I thought it was going to be."

Trump delivered an angry statement in the morning about what he called the "very unfair" partial gag order imposed by Merchan to prevent him from using his powerful media presence to attack witnesses, prosecutors, and relatives of court staff.

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"The judge has to take off this gag order," said Trump, who has a long history, including while president, of making threatening or insulting statements against private and public opponents.

On departure, he again called his trial a "giant witch hunt."

The court proceedings have disrupted Trump's 2024 campaign, but he has tried to use the press coverage to relay his claim to be the victim of a "hoax." On Saturday, he will hold a rally in North Carolina.

The Republican tycoon faces three other criminal cases, including far more serious charges of attempting to overturn his 2020 election loss to President Joe Biden, but these have been repeatedly delayed.