Donald Trump's New York criminal trial briefly descended into chaos Monday when the judge became infuriated by a defense witness's behavior and pandemonium broke out between journalists and court officers.

Lawyer Robert Costello, called up to testify by Trump's team, exasperated normally unflappable Judge Juan Merchan by constantly griping at his rulings.

Each time Merchan upheld a challenge from prosecutors to his statements on the stand, Costello would shake his head or sigh theatrically.

When Costello responded to another objection being upheld with an audible "Jeez!", Merchan snapped.

"Sorry?" the judge said, repeating more loudly: "Sorry?"

Merchan launched into a lecture on "proper decorum," saying that "if you don't like my ruling you don't say 'jeez,' you don't say 'stricken'. I am the only one who says that."

Yet Costello, unbowed, looked right back -- and now the judge had had enough.

"Are you staring me down?" Merchan said, incredulously. "Clear the courtroom!"

Trump -- accused of illegally covering up hush money paid to silence a porn star over an alleged sex encounter that he feared would wreck his 2016 election chances -- looked around his legal team.

And journalists, who have been covering the first criminal trial of a US president in history for weeks, hesitated to obey the judge.

"The public have a right to know," shouted one.

That prompted armed officers guarding the court to add to the yelling and order the reporters out -- even if Trump's large coterie of supporters were apparently allowed to remain.

A respected magistrate who moved with his Colombian parents to the United States when he was a child, Merchan has a reputation among lawyers for being fair but firm.

Throughout the historic trial, he has marshalled evidence from colorful witnesses including the former porn star Stormy Daniels, as well as protecting witnesses by fining Trump for previous outbursts and threatening him with jail if he further breaks a gag order.

The temperature seemed to have dipped after Merchan reopened the courtroom to the public and the press.

Though Costello looked chastened, blinking and flushed, he continued to grouse at the proceeding.

He later tried to fault the questions of Susan Hoffinger, the veteran prosecutor who asked him about his emails to Michael Cohen, a key prosecution witness.

"You misstated it, I was deputy chief of the criminal division," said Costello subsequently telling the experienced attorney to "talk into the microphone" when he had misheard a question, prompting stifled gasps from the courtroom.

His testimony continues Tuesday.