Donald Trump arrived at a Manhattan courthouse Monday for opening statements in his high-stakes criminal trial, the first ever of a former president, with proceedings set to run in parallel with his attempt to retake the White House.

The historic case poses substantial risks for Trump less than seven months before his election rematch with President Joe Biden.

Prosecution witnesses are expected to include adult film actress Stormy Daniels - who says she had a sexual encounter with Trump in 2006, a claim he denies - and Trump's former fixer Michael Cohen, offering an insight into the 77-year-old tycoon's personal and business habits.

The identities of the jury's five women and seven men are being kept secret for their own protection.

Security was tight Monday after a man set himself on fire last week outside the courthouse in an unrelated but gruesome incident.

Trump faces 34 counts of falsifying business records as part of a scheme to pay $130,000 in "hush money" to Daniels to ensure an account of their alleged tryst did not get published ahead of the 2016 presidential election.

The alleged crime is less significant than the indictments in three other investigations revolving around Trump's attack on the 2020 election - which the Republican lost to Democrat Biden - and his hoarding of secret documents.

Trump could face jail time in the current case, although a fine or probation is more likely, analysts say.

The trial in a dingy courtroom under massive media scrutiny will keep Trump off the campaign trail for four days a week over a possibly six-to-eight-week period, while Biden hammers him from the White House and around the country.

Monday is expected to see each camp to lay out their case to jurors and mount preemptive attacks on the opposing side's witnesses.

"This is going to be the beginning of probably the most sensational trial in American history," former prosecutor Bennett Gershman, now a lecturer at Pace University, told AFP.

"The stakes are almost infinite in terms of what the consequences could be... Every day we're going to be hearing testimony that's going to be damaging to Mr Trump."

Trump rants

Trump has railed against the case, particularly what he calls the "very unfair" partial gag order imposed by Judge Juan Merchan to prevent him from using his media presence to attack witnesses, prosecutors and relatives of court staff.

He ranted again overnight, taking to his Truth Social platform to decry the "Corrupt and Highly Conflicted Judge" overseeing the case.

"It is a sham that should not have been brought, except to try and damage Biden's political opponent, me," Trump wrote in capital letters.