The twin 7-2 rulings authored by conservative Chief Justice John Roberts mark another milestone in Trump's tumultuous presidency and in the short term prevent details of his finances from becoming public because lower courts must resolve lingering issues.

The businessman-turned politician, seeking re-election on November 3, has fought tenaciously to keep his tax returns and other elements of his finances secret - and the rulings spare him of any major revelation at a sensitive time. But looking further ahead, Trump faces possible future criminal prosecution in his native New York, perhaps after he leaves office.

The Supreme Court emphasised that there are limits to the powers of the presidency and stoutly reaffirmed the principle that not even the president is above the law - a message delivered 3-1/2 years into a presidency in which Trump has repeatedly skirted the norms of American political conduct.

Trump's two Supreme Court appointees, conservatives Neil Gorsuch and Brett Kavanaugh, joined Roberts and the four liberal justices in both rulings, spurning Trump's arguments that the Constitution gave him absolute immunity from any criminal proceedings as a sitting president.

Manhattan District Attorney Cyrus Vance, a Democrat, and the three House committees all issued subpoenas to third parties for the records, not to the Republican president himself. Trump sued to block enforcement of the subpoenas.

The court in the New York case ruled that the subpoena to Trump's long-term accounting firm, Mazars LLP, for tax returns and other financial records to be turned over to a grand jury as part of Vance's criminal investigation can be enforced.

The justices rebuffed Trump's broad arguments on expansive presidential powers in a showdown with Congress as he tried to block subpoenas by lawmakers to Mazars and two banks - Deutsche Bank and Capital One - for his financial records. In doing so, the court also faulted the broad arguments made by the House and sent the litigation back to lower courts, delaying the final outcome.

Trump portrayed himself as a victim, calling the subpoenas a "pure witch hunt" and a "hoax" in comments to reporters. On Twitter, he wrote, "This is all a political prosecution ... and now I have to keep fighting in a politically corrupt New York. Not fair to this Presidency or Administration!"

Trump's argument that he was immune from any criminal process "runs up against the 200 years of precedent establishing that Presidents, and their official communications, are subject to judicial process," Roberts wrote.

"We affirm that principle today and hold that the president is neither absolutely immune from state criminal subpoenas seeking his private papers nor entitled to a heightened standard of need," Roberts added.

Roberts rejected the suggestion that the decision would subject future presidents to harassment by local prosecutors, noting that the court in 1997 rejected a similar argument made by President Bill Clinton when he faced a civil lawsuit brought by a woman who accused him of making unwanted sexual advances - litigation the court refused to delay.

The court in 1974, Roberts noted, also ruled that President Richard Nixon must turn over audio tapes in the Watergate scandal that eventually drove him to resign.

'Unlike other recent presidents, Trump has refused to release his tax returns and other documents that could provide details on his wealth and the activities of his family real-estate company, the Trump Organisation.

Australian Associated Press