Stormy Daniels, the porn star at the heart of Donald Trump's historic criminal trial, testified Tuesday – in sometimes explicit detail – about an alleged 2006 sexual encounter with the former president in a hotel penthouse suite.

Trump, 77, is accused of falsifying business records to reimburse his lawyer, Michael Cohen, for a $130,000 hush money payment to Daniels on the eve of his 2016 election against Hillary Clinton, when the lurid story of marital infidelity could have sunk his campaign.

"The people call Stormy Daniels," prosecutor Susan Hoffinger announced as Trump, who is seeking to recapture the White House in November, sat at the defence table in the Manhattan courtroom flanked by his lawyers.

What followed was detailed testimony about the sexual encounter Daniels said she had with Trump - his pajamas, his boxer shorts, the sexual position, that he did not wear a condom – all while the former president, sitting just feet away, stared on in silence, stony-faced.

Trump has always categorically denied having sex with the actress.

The extraordinary courtroom face-off comes six months before election day when Trump will try to defeat Democratic President Joe Biden.

Daniels, wearing a black pantsuit, walked prosecutors through her difficult childhood in Louisiana, a stint as a stripper and eventually joining the adult film industry.

The 45-year-old, whose real name is Stephanie Clifford, said she met Trump at a celebrity golf tournament in Lake Tahoe where she was employed as a greeter by X-rated movie company Wicked Entertainment.

Trump complimented her as the "smart one" because she was not only acting in adult movies but also directing them, she said.

Daniels said she was 27 at the time and Trump was "probably older than my father."

She said a member of Trump's security detail told her the real estate tycoon wanted to have dinner with her. She was reluctant but agreed after discussing it with her publicist.

When she arrived at the penthouse where Trump was staying he emerged wearing "silk or satin pyjamas which I immediately made fun of," Daniels told the jury.

"I said 'Does Mr Hefner know you stole his pyjamas?'" she said in a reference to the outfit favoured by the late Playboy magazine founder Hugh Hefner.

Trump changed clothes and they began talking about adult movies.

"He was very interested in a lot of the business stuff," Daniels said.

Trump, who was married at the time to his current wife, Melania, suggested at one point that Daniels should be on his hit reality television show, The Apprentice, she said.

"I said there's no way NBC would let me on television," Daniels added.

'Startled me'

Daniels said she went to the bathroom at one point and when she emerged Trump was on the bed in boxer shorts and a T-shirt.

"It startled me," she said. "The intention was pretty clear."

"I was not threatened verbally or physically," Daniels said, although there was an "imbalance of power."

She said they had brief sex on the bed "in missionary position" and Trump did not wear a condom.

"I felt ashamed I didn't stop it, didn't say no," Daniels said.

Daniels said she met with Trump again on several occasions but cut off contact when it became clear she was not going to secure a spot on The Apprentice.

After Trump announced his candidacy for president, Daniels said her publicist Gina Rodriguez suggested she could sell her story and put her in touch with Keith Davidson, a Hollywood lawyer who testified previously at the trial.

"My motivation wasn't money, it was to get the story out," Daniels said.

She said she entered into a non-disclosure agreement in October 2016 on the eve of the presidential election negotiated by Davidson and Cohen for which she was paid $130,000.

"I couldn't tell my story, he couldn't tell the story," she said.

Gag order

Trump is under a partial gag order from presiding Judge Juan Merchan prohibiting him from publicly attacking witnesses, the jury or court staff.

Merchan has fined him $10,000 so far for breaching the gag order and has warned Trump he may face jail time for future violations.

In addition to the New York case, Trump has been indicted in Washington and Georgia on charges of conspiring to overturn the results of the 2020 election he lost to Biden.

He also faces charges of illegally storing top-secret documents taken from the White House at his home in Florida and refusing to return them.