The judge overseeing Donald Trump’s criminal “hush money” trial has fined the former US president $US9,000 ($A13,842) for violating a gag order and said he would consider jailing him if he continued to breach it.

In a written order, Justice Juan Merchan said the fine may not be enough to serve as a deterrent for the wealthy businessman-turned-politician and lamented that he did not have the authority to impose a higher penalty.

“Defendant is hereby warned that the Court will not tolerate willful violations of its lawful orders and that if necessary and appropriate under the circumstances, it will impose an incarceratory punishment,” he wrote.

Justice Merchan had imposed the gag order to prevent Trump from criticising witnesses and others involved in the case.

The fine was just short of the $US10,000 penalty that prosecutors had requested for 10 posts that insulted likely witnesses and questioned the impartiality of the jury. Justice Merchan found nine posts breached the order.

The order came as the trial was due to resume in New York with testimony from a banker familiar with accounts involved in Mr Trump’s alleged scheme to influence the 2016 election by covering up a sex scandal.

Justice Merchan will consider whether to impose further fines for other statements at a hearing on Thursday.

He also ordered Mr Trump to remove the statements from his Truth Social account and his campaign website.

Mr Trump, the Republican candidate in the 2024 presidential election, is charged with falsifying business records to conceal a $US130,000 payment to adult film star Stormy Daniels in exchange for her silence about a sexual encounter she said she had with Mr Trump in 2006.

Mr Trump has pleaded not guilty and denied having sex with Ms Daniels, whose real name is Stephanie Clifford.

The historic criminal trial is the first of a former US president and began on April 22.

Roughly two dozen Trump supporters rallied outside the courthouse on Tuesday morning, chanting his name and waving banners that read “TRUMP 24”.

A local Republican organisation had called for supporters to turn out after Mr Trump complained that few people were protesting the trial.

Banker Garry Farro, who is not accused of wrongdoing, testified on Friday about financial records filed by Mr Trump’s one-time lawyer and fixer Michael Cohen, who prosecutors say helped carry out the scheme.

Mr Trump is required to attend the trial and has said he could instead be campaigning ahead of his rematch with Democratic President Joe Biden in the November 5 election.

The criminal case is one of four pending against Mr Trump, but could be the only one to go to trial and result in a verdict before the election.

Reuters/ABC