Judge appoints monitor for Trump company

A New York judge has ordered that an independent watchdog be appointed to oversee the Trump Organization before a civil fraud case by the state's attorney-general against Donald Trump's company goes to trial.

Justice Arthur Engoron's decision came in state Attorney-General Letitia James's $US250 million ($A397 million) lawsuit accusing the Republican former president, his company and three of his children of overvaluing assets and Trump's net worth through a decade of lies to banks and insurers.

Last month, James asked the Manhattan-based judge to appoint a monitor to halt ongoing fraud at the company and keep the Trumps from transferring assets out of her reach.

Engoron called appointing a monitor "the most prudent and narrowly tailored mechanism to ensure there is no further fraud or illegality", citing "persistent misrepresentations" in Trump's statements of financial condition from 2011 to 2021.

Trump blasted what he called Engoron's "ridiculous" decision, one day after suing James, a Democrat, in a Florida court to stop what Trump labelled her "inquisition".

The decision bars the defendants from transferring assets without court approval, and requires the monitor receive a "full and accurate description" of the company's structure and assets.

Engoron said his scepticism was bolstered by Trump's decision to invoke his right against self-incrimination more than 400 times when questioned under oath by James's office in August.

James called the decision a "major victory" that would stop Trump and his companies continuing "the extensive fraud that we uncovered".

Both sides have until November 10 to recommend three candidates to become a monitor.

The judge's decision focused on several alleged instances of fraud, including Trump's claim that his penthouse in Manhattan's Trump Tower was nearly triple its actual size, giving it an inflated $US327 million valuation in 2015. No apartment in Manhattan has sold for that much.

"You said experts can disagree" on valuation, the judge told Christopher Kise, a lawyer for Trump at a hearing on Thursday. "But does there reach a point it's just not a disagreement ... but bad faith?"

Kise argued that James's demand for a monitor was a "manufactured emergency" before next Tuesday's midterm election.

He said James had no legal authority to challenge how Trump valued his properties, calling it a private matter between Trump's company and its lenders and insurers.

Kevin Wallace, a lawyer from James's office, countered that it was important to the public to maintain an "honest and fair business environment".

The Trump Organization manages hotels, golf courses and other real estate around the world.

James sued the company and Trump's family in September after a three-year probe.

The case is among many legal battles Trump faces as he mulls a 2024 bid for the presidency.

Testimony also began this week in a criminal case by the Manhattan district attorney's office accusing the Trump Organization of scheming to defraud tax authorities for at least 15 years.