A judge overseeing Donald Trump’s civil fraud trial has pounded his fists in frustration with the former US president’s lawyers for what he described as redundant and “ridiculous” cross-examination of a witness.

The heated exchange occurred on Wednesday, the third day of trial in a lawsuit by the New York attorney-general’s office that threatens to dismantle Trump’s business empire over allegations that he inflated his net worth by billions of dollars to secure better loan and insurance terms.

On Tuesday, Justice Arthur Engoron imposed a gag order on public statements about court staff after Trump took to social media to lash out at the judge’s top law clerk.

Trump, the frontrunner for the 2024 Republican presidential nomination, has denied wrongdoing and said the case is part of a political witch hunt.

Engoron alone will decide the outcome of the trial. There is no jury. He has already disciplined Trump’s lawyers for making what he said were “frivolous” arguments.

“This is ridiculous,” Engoron said on Wednesday as one of Trump’s lawyers repeatedly asked his one-time accountant the same questions for each year at issue in the case.

“All I’m asking is that you lump things together so we do not waste time,” Engoron said.

Trump, who was in court for the third straight day, has repeatedly attacked New York Attorney-General Letitia James and Engoron in remarks to media outside the courtroom, calling them “corrupt” and decrying the case as a “fraud and a sham”.

“He already knows what he’s going to do,” Trump said of Engoron on Wednesday.

Engoron ruled last week that Trump, his two adult sons and 10 of his companies committed fraud by inflating the value of their assets.

The judge cancelled the business certificates for companies controlling jewels of Trump’s portfolio, including Trump Tower and 40 Wall Street in Manhattan. He said would appoint receivers to oversee the dissolution of those entities.

Trump’s lawyers appealed the decision on Wednesday.

The trial, which is expected to run through mid-December, largely concerns damages.

James, a Democrat, is seeking at least $US250 million ($A395 million) in fines, a permanent ban against Trump and his sons Donald Jr. and Eric from running businesses in New York, and a five-year commercial real estate ban against Trump and the Trump Organisation.

Trump also faces four criminal indictments over his attempts to overturn Democrat Joe Biden’s 2020 presidential election victory, his handling of classified documents after he left the White House, and hush money paid to pornographic actress Stormy Daniels.

Trump has denied wrongdoing and pleaded not guilty in all of the cases. He also faces a January civil damages trial for defaming a writer who accused him of rape, which he denies.

The government cases have strengthened Trump politically, and his campaign is using them to raise money by portraying him as a martyr.

– AAP