A former Playboy model who said she had an affair with US President Donald Trump has filed a lawsuit to release her from a legal agreement requiring her to stay silent.

Karen McDougal filed the suit in Los Angeles Superior Court against American Media, publisher of the National Enquirer, which paid her $US150,000 ($195,000) in 2016 to keep quiet on the matter, according to a copy of the lawsuit provided by her lawyer, Peter Stris.

The lawsuit comes a month after the New Yorker reported on the alleged affair and a move by American Media to pay Ms McDougal for exclusive rights to her story, which it never published.

The New Yorker article noted that American Media head David Pecker has described Mr Trump as a “personal friend”.

“AMI lied to me, made empty promises, and repeatedly intimidated and manipulated me,” Ms McDougal, who was Playboy magazine’s 1998 Playmate of the Year, said in a statement on Tuesday.

“I just want the opportunity to set the record straight and move on with my life, free from this company, its executives, and its lawyers.”

It comes as a New York state judge has said President Trump must face a defamation lawsuit by a woman who accused him of sexually harassing her after she appeared on his former reality TV show.

The decision by Justice Jennifer Schecter of the New York state court in Manhattan in favour of California restaurateur Summer Zervos, a former contestant on NBC’s The Apprentice, raises the prospect that Mr Trump might have to publicly answer questions in court about his behaviour towards women.

A lawsuit brought by ex-The Apprentice contestant Summer Zervos against Donald Trump will proceed. Photo: Getty

Justice Schecter rejected Mr Trump’s claim that he was immune from being sued, finding “absolutely no authority” to dismiss litigation related “purely to unofficial conduct” solely because he occupied the White House.

“No one is above the law,” the judge wrote.

A White House representative was not immediately available for comment on the ruling.

Mariann Wang, one of Ms Zervos’ lawyers, said in a statement on Tuesday: “We are grateful for the opportunity to prove that that defendant falsely branded Ms Zervos a phoney for telling the truth about his unwanted sexual groping.”

Mr Trump has been accused by several women of misconduct, including after the release during the 2016 presidential campaign of an Access Hollywood recording in which he had spoken in vulgar terms about trying to have sex with women.

He later said the comments were “locker room banter” and his campaign issued an apology from him if anyone was offended.

Adult film actress Stormy Daniels, whose real name is Stephanie Clifford, sued the president on March 6, stating that Mr Trump never signed an agreement for her to keep her quiet about an “intimate” extramarital relationship between them.

Ms Daniels received $US130,000 ($168,000) under that agreement.

Earlier this week, a law firm representing Mr Trump and the corporation that paid Ms Daniels said in a court filing it was seeking at least $US20 million ($25 million) in damages for multiple violations of the non-disclosure agreement.