Donald Trump’s former personal lawyer Michael Cohen has described the US President as a “racist”, a “conman” and a “cheat” in an explosive testimony before Congress on Thursday morning (Australian time).

Speaking under oath, Cohen told the Oversight and Reform Committee that Mr Trump had advance notice of WikiLeaks’ release of emails damaging to Hillary Clinton’s 2016 presidential election campaign.

The former Trump insider also told the hearing, which continues Thursday, that Mr Trump directed negotiations for a real estate project in Moscow, even as he publicly said he had no business interests in Russia and while he campaigned for the presidency.

Trump’s former lawyer, Michael Cohen, opened his testimony with fiery words against the president.

“He's a racist. He's a conman. And he's a cheat… The last time I appeared before Congress, I came to protect Mr. Trump. Today, I'm here to tell the truth” https://t.co/5ZDngh3jwc pic.twitter.com/C7ypUQVgev

— POLITICO (@politico) February 27, 2019

Cohen said Mr Trump ordered him to pay US$130,000 ($181,005) to adult film actress Stormy Daniels to cover up an affair, in violation of campaign finance laws, and also told Cohen to lie about it to First Lady Melania Trump.

Cohen produced a cheque signed by Mr Trump he said was offered as repayment for the hush money.

“I am ashamed of my weakness and misplaced loyalty, of the things I did for Mr Trump in an effort to protect and promote him,” Cohen said.

“I am ashamed that I chose to take part in concealing Mr Trump’s illicit acts rather than listening to my own conscience. I am ashamed because I know what Mr Trump is,” he said.

Cohen tendered a cheque he says proves Mr Trump paid hush money. Photo: Getty

Republicans on the House committee focused on assailing Cohen and his credibility.

Accused by one Republican politician of being a pathological liar, Cohen responded: “Sir, are you referring to me or the president?”

Cohen’s claim that Mr Trump had advance knowledge of WikiLeaks’ release of Democratic National Committee (DNC) emails regarding Mrs Clinton is a direct contradiction of the President’s previous assertions.

Cohen said he was in Mr Trump’s office in July 2016 when political adviser Roger Stone called the Republican presidential candidate.

He said Stone told Mr Trump he had been speaking with WikiLeaks founder Julian Assange, who told him there would be a dump of emails within a couple of days that would damage Mrs Clinton’s campaign.

Mr Trump responded by saying “wouldn’t that be great,” Cohen said.

On July 22, 2016, WikiLeaks released internal DNC emails that drove a wedge between supporters of Mrs Clinton’s Democratic rival Senator Bernie Sanders. 

The damning testimony comes as Special Counsel Robert Mueller is expected to soon complete his investigation into possible collusion between the Trump election campaign and Russian efforts to interfere in the 2016 election.

Mr Trump, who has denied any collusion between his campaign and Moscow, has repeatedly dismissed the Mueller probe as a “witch hunt” and has said Cohen is a liar and a “rat”.

“He did bad things unrelated to Trump. He is lying in order to reduce his prison time,” Mr Trump tweeted Wednesday from Vietnam, where he was meeting with North Korean leader Kim Jong Un.

Michael Cohen was one of many lawyers who represented me (unfortunately). He had other clients also. He was just disbarred by the State Supreme Court for lying & fraud. He did bad things unrelated to Trump. He is lying in order to reduce his prison time. Using Crooked’s lawyer!

— Donald J. Trump (@realDonaldTrump) February 27, 2019

Later, sitting alongside Mr Kim, the President refused to answer reporters’ questions about Cohen, who has already been sentenced and begins a three-year prison term in May after pleading guilty to multiple crimes.

A judge already has set Cohen’s sentence, and the Congressional testimony will have no bearing on that term.

Ahead of the hearing, Cohen said that the US public could decide “exactly who is telling the truth” when they heard his testimony.

-with agencies