Donald Trump's criminal trial on charges stemming from hush money paid to a porn star is not a referendum on his presidency, a prosecutor told prospective jurors on Tuesday in asking whether they could put personal politics aside.

"This case is really not about whether you like Donald Trump. This case is about the rule of law and whether Donald Trump broke it," Manhattan Assistant District Attorney Joshua Steinglass told the 18 prospective jurors who remained of an initial pool of 96.

Jury selection for the former US president's trial got under way on Monday. He faces 34 felony counts of falsifying business records to cover up a hush money payment to porn star Stormy Daniels shortly before the 2016 election. Daniels says she had a sexual encounter with Trump about a decade beforehand.

Trump has pleaded not guilty and denies an encounter took place. The Republican presidential candidate has called the case, brought by Democratic Manhattan District Attorney Alvin Bragg, a partisan witch hunt meant to interfere with his campaign to unseat President Joe Biden, a Democrat, in the November 5 election.

The hush money case is one of four criminal indictments he faces, which stem from alleged mishandling classified information and trying to overturn his 2020 loss to Biden. He has pleaded not guilty in those cases, which may not go to trial before the election.

The proceedings so far have underscored the challenges of choosing a jury of 12 residents of heavily Democratic Manhattan who can try the case fairly and impartially.

Roughly half of 96 potential jurors summoned on Monday were dismissed after saying they could not impartially judge the polarising businessman-turned-politician.

Six more were excused on Tuesday. They said they had scheduling conflicts, concerns about balancing juror service with their jobs, or had thought further overnight and come to the conclusion they could not be fair.

The jurors allowed to stay on for now after answering questions on Tuesday included an asset manager at Lazard who is originally from Mexico and enjoys scuba diving and skiing, and a corporate lawyer from Oregon who hikes and runs in his spare time and reads the New York Times and the Wall Street Journal.

Trump, wearing a blue tie, at times held a piece of paper up to his face as jurors read out answers to a list of 42 questions. Occasionally he yawned and leaned back in his chair at the defence table. (Reuters)