NEW YORK - Donald Trump Jr, former President Donald Trump's eldest son, took the witness stand on Wednesday at the New York civil fraud trial accusing the family business of inflating asset values.

Donald Trump Jr., an executive vice president at the Trump Organization, is the first member of the Trump family to testify in the case.

New York Attorney General Letitia James has accused the former president, his adult children and a handful of their family businesses of inflating their assets by billions of US dollars to secure better loan terms.

During the trial, Donald Trump Jr. said that he and his younger brother, Eric Trump, largely took over management of the company after their father assumed the presidency in 2017, but he denied any wrongdoing in the case.

Donald Trump Jr. is expected to continue his testimony on Thursday, followed by Trump's other adult children - Eric and Ivanka.

Before his elder son's testimony, Trump blasted Judge Arthur Engoron, who is presiding over the case, Wednesday on social media platform Truth Social, calling him a "political hack".

"Engoron is crazy, totally unhinged, and dangerous," the former president wrote. "Leave my children alone, Engoron. You are a disgrace to the legal profession!"

The civil fraud trial is one of several legal troubles Trump faces, who is a frontrunner in the presidential campaign, as he seeks to recapture the White House.

Trump is also under a limited gag order barring him from speaking publicly about court staff in the case, and he has been fined 15,000 dollars for attacking Judge Engoron's top clerk.