The US President’s personal lawyer Michael Cohen has made the ‘staggering’ decision to refuse to give evidence in the lawsuit brought against him by adult-film star Stormy Daniels.

In a filing in Los Angeles federal court on Thursday (Australian time), Mr Cohen said he would plead the Fifth Amendment because he feared saying something that might incriminate him in a separate criminal probe.

The FBI raided his home, office and hotel room two weeks ago, reportedly on suspicion of bank fraud, wire fraud and campaign finance violations.

Ms Daniels sued Mr Trump and Mr Cohen last month to end a non-disclosure agreement related to a $US130,000 ($171,000) payment she received from Mr Cohen before the 2016 election to keep quiet about her alleged affair with Mr Trump a decade earlier.

In a civil case the person being sued would normally be deposed by lawyers for the claimant in a lengthy question and answer session. False answers given in these sessions carry the same penalty as lying to a judge.

Mr Avenatti said the decision was a “big deal”. Photo: MSNBC

Michael Avenatti, the lawyer for Ms Daniels, said it was a “staggering development” given that Mr Trump had deflected questions to his lawyer.

“You’ll have to ask Michael Cohen,” was Mr Trump’s reply days earlier when asked on Air Force One if allegations of hush money were untrue.

“That same individual that the President pointed … members of the media and the American people to for answers is now refusing to provide those answers and claiming he can’t answer those questions because the answers will incriminate him,” Mr Avenatti told MSNBC.

“This is a staggering development. It cannot be over exaggerated, it cannot be overstated. This is a big deal.”

Mr Avenatti threatened to depose Mr Trump himself much sooner than originally planned if the court permits Mr Cohen to avoid giving evidence.

What this may result in, quite frankly, is we may be able to take the deposition of the President first rather than second.”

If Mr Trump also pleaded the Fifth, it would be an “even more staggering development,” the lawyer said.

“Imagine if the President of the United States, the sitting president, invoked his fifth amendment rights in an effort to avoid answering questions about this agreement, the $130,000, what he knew, when he knew it, the cover up.”

Mr Cohen’s decision to plead the Fifth Amendment was in support of his request for a 90-day delay to the Daniels case.

At a hearing last week on the delay, US District Judge James Otero said he needed more time to consider the request but warned there were “some gaping holes”.

Lawyers for Mr Trump and Mr Cohen have said Ms Daniels’ civil lawsuit overlaps the criminal probe of Mr Cohen’s business affairs.

They argue that letting her case proceed could both impair his constitutional right against self-incrimination and make it harder for Mr Trump to defend himself.

Ms Daniels hijacked the first day of Mr Cohen’s hearing. Photo: Getty

Photographers knocked over barricades outside court last week as they scrambled to get pictures of Ms Daniels, whose real name is Stephanie Clifford, when she appeared at the first day of Mr Cohen’s hearing.

Mr Cohen fronted court to protest against the seizure of documents from his firm relating to the US President.

Ms Daniels, who was not party to the proceedings, decided to show up and call a press conference over an unrelated dispute she has with Mr Cohen.

She staged a brief and fiery press conference outside the courtroom, accusing Mr Cohen of acting for years “like he is above the law” and of acting as “Mr Trump’s fixer”.

“He has played by a different set of rules or should we say no rules at all,” Ms Daniels told reporters.

“He has never thought that the little man, or especially women and even more, women like me, mattered. That ends now.”

-with AAP