He also says Trump directed him to arrange the payment of hush money to porn star Stormy Daniels and a former Playboy model to fend off damage to his White House bid.

Cohen's extraordinary account marks the first time that any Trump associate has gone into open court and implicated Trump himself in a crime, though whether - or when - a president can be prosecuted remains a matter of legal dispute.

The guilty plea was part of a double dose of bad news for Trump: It came at almost the same moment his former campaign chairman Paul Manafort was convicted in Alexandria, Virginia, of eight financial crimes in the first trial to come out of special counsel Robert Mueller's sprawling Russia investigation.

In a deal reached with federal prosecutors, Cohen, 51, pleaded guilty to eight counts , including tax evasion. He could get about four to five years in prison at sentencing Dec. 12.

In entering the plea, Cohen did not name the two women or even Trump, recounting instead that he worked with an "unnamed candidate" to influence the election.

But the amounts and the dates all lined up with the $US130,000 paid to Daniels and the $US150,000 that went to Playboy Playmate Karen McDougal to buy their silence in the weeks and months leading up to the 2016 presidential election. Both women claimed to have had affairs with Trump, which he denies.

Cohen, his voice shaky as he answered questions from a federal judge, said one payment was "in coordination and at the direction of a candidate for federal office," and the other was made "under direction of the same candidate."

However, in the charging documents, a news release and comments outside the courthouse, prosecutors did not go as far as Cohen did in open court in pointing the finger at the president. Prosecutors said Cohen acted "in coordination with a candidate or campaign for federal office for purposes of influencing the election."

Trump's personal lawyer, Rudy Giuliani, noted in a statement that "there is no allegation of any wrongdoing against the president in the government's charges against Mr. Cohen."

Daniel Petalas, a former prosecutor in the Justice Department's public integrity section, said, "This brings President Trump closer into the criminal conduct."

"The president has certain protections while a sitting president, but if it were true, and he was aware and tried to influence an election, that could be a federal felony offense," Petalas said. "This strikes close to home."

After the court hearing, which ended with Cohen released on $US500,000 bail, the lawyer wiped away tears as he gazed out a courthouse window. He left the building and headed straight for a black SUV with tinted windows. A couple of people outside chanted, "Lock him up!" as they recorded the scene with their phones.

Under federal law, expenditures to protect a candidate's political fortunes can be construed to be campaign contributions, subject to federal laws that bar donations from corporations and set limits on how much can be given.

Australian Associated Press