Former US president Donald Trump arrived in court on Monday for opening statements in his criminal trial and condemned the high-stakes case as a "witch hunt" designed to derail his White House bid.

"It's a very, very sad day in America," the 77-year-old Republican presidential candidate told reporters before entering the Manhattan courtroom.

"I'm here instead of being able to be in Pennsylvania, in Georgia, and lots of other places campaigning," he said. "This is a witch hunt and it's a shame and it comes out of Washington."

Trump is the first former president to face criminal charges and the case poses substantial risks to him 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.

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

Security was tight on 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 US$130,000 in "hush money" to Daniels to ensure an account of their alleged tryst did not get out ahead of the 2016 presidential election.

The alleged crime is less significant than the indictments stemming from 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. (AFP)