PROSECUTORS slammed US President Donald Trump’s disgraced former campaign chairman Paul Manafort during the first day of his trial, labelling him as a man who considered himself above the law.

Manafort is facing tax evasion and bank fraud charges, and is accused of opening more than 30 bank accounts in three foreign countries to “receive and hide” income.

His crimes could carry a sentence of 300 years in prison if he is convicted.

During his time as a lobbyist where he worked for a former pro-Russia politician in Ukraine, prosecutors said Manafort lived an “extravagant lifestyle” funded by “secret income”.

“A man in this courtroom believed the law did not apply to him. Not tax, not banking law,” said prosecutor Uzo Asonye, a member of Special Counsel Robert Mueller’s team looking at Russian election meddling and whether any Trump campaign members co-ordinated with Moscow officials.

Manafort’s trial is the first to result from special counsel Robert Mueller’s investigation into potential ties between the Trump presidential campaign and Russia.

A spendthrift Manafort snapped up expensive cars and watches, according to Asonye, and acquired real estate in New York and Virginia worth $6 million ($A8 million).

He even spent $15,000 ($A20,000) on a jacket “made from an ostrich”, Asonye said.

Manafort’s defence lawyer Thomas Zehnle said the Ukrainian oligarchs the former campaign manager worked for were to blame, CNN reported.

Mr Zehlne said it was “the way that they required it to be done”, when explaining why the oligarchs paid Manafort via secret overseas bank accounts.

The defence also made clear he would go after one of the government’s star witnesses, former Manafort associate Rick Gates.

Gates pleaded guilty for his involvement in Manafort’s alleged financial rort, and is expected to testify against him.

Six men and six women, along with four alternate jurors, were chosen for the trial.

Mr Manafort, who is already in custody and could spend the rest of his life in jail, appeared in the federal courtroom in Alexandria, Virginia, in a dark suit with his wife, Kathleen.

Mr Manafort’s case is widely viewed as a test to the legitimacy of Mr Mueller’s probe, which Mr Trump has called a “witch hunt.”

His conviction would give momentum to Mueller, who has indicted or secured guilty pleas from 32 people and three companies since the probe started 14 months ago.

Protesters appeared outside the courthouse where Mr Manafort appeared, yelling out “lock him up”.

TRUMP: COLLUSION IS NOT A CRIME

It came as Mr Trump seemed to change his legal defence, tweeting that “collusion is not a crime”.

“Collusion is not a crime, but that doesn’t matter because there was No Collusion (except by Crooked Hillary and the Democrats)!” Mr Trump wrote on Twitter.

While collusion is not a technical legal charge, Mr Mueller could bring conspiracy charges if he believes there was such work by campaign members with Russia.

Mr Trump’s lawyer, former New York City mayor Rudy Giuliani did a round of interviews on Sunday, presenting what many believed to be a new legal defence — that collusion isn’t a crime.

“You start analysing the crime, the hacking is the crime. The hacking is the crime,” he concluded. “Well the president didn’t hack. He didn’t pay them for hacking.”

Mr Trump has denied that the campaign worked with Russia to engineer his victory against Democratic candidate Hillary Clinton and bristles at the suggestion he might owe his White House victory to Moscow. Moscow has denied any meddling in the election.

Mr Manafort, 69, faces 18 criminal counts, which centre on allegations that he hid much of the $US60 million ($A81 million) he earned working for a pro-Russia politician in Ukraine in undisclosed overseas bank accounts and failed to pay taxes on it.