Tuesday's outcome, which was widely expected, could prompt House Ways and Means Committee Chairman Richard Neal to subpoena Trump's tax records as the opening salvo to a legal fight that may ultimately have to be settled by the US Supreme Court.

Neal set a final 5pm deadline for the Internal Revenue Service and Treasury to provide six years of Trump's individual and business tax records. But the deadline passed without the panel receiving the documents.

After the deadline lapsed, Mnuchin released a letter to Neal in which he pledged to make "a final decision" on whether to provide Trump's tax records by May 6.

It was the second time the administration had missed a House deadline for the tax returns since Neal requested them on April 3.

"Secretary Mnuchin notified me that once again, the IRS will miss the deadline for my ... request. I plan to consult with counsel about my next steps," Neal said in a statement.

In his letter, Mnuchin said he was still consulting with the Justice Department about Neal's request, which he termed "unprecedented."

"The department cannot act upon your request unless and until it is determined to be consistent with the law," the Treasury secretary told Neal.

Democrats want Trump's returns as part of their investigations of possible conflicts of interest posed by his continued ownership of extensive business interests, even as he serves the public as president.

Republicans have condemned the request as a political "fishing expedition" by Democrats.

Trump broke with a decades-old precedent by refusing to release his tax returns as a presidential candidate in 2016 or since being elected, saying he could not do so while his taxes were being audited.

But his former personal lawyer, Michael Cohen, told a House panel in February that he did not believe Trump's taxes were under audit. Cohen said the president feared that releasing his returns could lead to an audit and IRS tax penalties.

Earlier on Tuesday, the White House said Trump was unlikely to hand over his tax returns.

"As I understand it, the president's pretty clear: Once he's out of audit, he'll think about doing it, but he's not inclined to do so at this time," White House spokesman Hogan Gidley told Fox News in an interview.

"This is not up to the president. We did not ask him," said a Democratic committee aide, who cited a law saying the Treasury secretary "shall furnish" taxpayer data upon request from an authorised lawmaker.

Legal experts said House Democrats could vote to hold Mnuchin or Rettig in contempt of Congress if they ignored a subpoena, as a pretext to suing in federal court to obtain Trump's returns.

Experts say administration officials could ultimately risk financial penalties and even jail time by defying the committee.

Australian Associated Press