New York, New York - Former President Donald Trump was back in court on Thursday for his New York civil trial on fraud allegations, once again condemning the process as unfair.

Trump, the frontrunner for the 2024 Republican presidential nomination, and his two eldest sons are accused of inflating the value of their real estate assets to receive more favorable bank loans and insurance terms.

Trump lashed out on social media ahead of the hearing, saying his "case was decided against me before it even started."

During the trial, Trump has called the judge in the case, Arthur Engoron, "crazy" and "unhinged" and denounced New York state Attorney General Letitia James, who is Black, as "corrupt" and "racist."

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Trump, who testified on November 6 and is expected to again take the witness stand on December 11, was in court as a spectator on Thursday.

He wore a dark blue suit with a red tie and decried the process as he made his way into court. "This is a witch hunt, and it's a very corrupt trial," he told reporters.

Inside, Trump flipped through papers while his legal team questioned a witness on the stand, accountancy professor Eli Bartov, who gave evidence to support Trump's case that he had not inflated his worth.

Bartov said James' complaint had no merit because "accounting is rule-based... some of the allegations border on the absurd."

"3 or 4% of companies report that they had errors in their financial reporting. Financial errors are normal. This is inevitable," Bartov said. "If you do fraudulent misstatement, you'll do everything you can to conceal this misstatement... there is no concealment."

Bartov argued balance sheet rules meant that Trump's true value was understated because intangible assets were not included.

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"There is no question that the brand value of Mr Trump is worth billions... but it's nowhere to be found on the statement of financial condition," the professor said.

Bartov snapped at the attorney general's legal team when they claimed that some of his testimony was pure speculation. "You really ought to be ashamed of yourself," he said.

Trump was joined in court by his son Eric, who is also a defendant in the trial. The former president said on social media that Eric would not testify again as he had "already testified PERFECTLY."

The former president will stand trial on March 4 in Washington in a federal case in which he is accused of seeking to upend the results of the 2020 election in a concerted effort that led to the violent January 6, 2021, attack on the Capitol by his supporters.

Trump also faces federal charges for allegedly mishandling top secret documents after he left the White House and has been charged with racketeering in Georgia on accusations that he tried to overturn the 2020 election results in the southern state.