Woes mount for Trump

Donald Trump's presidential hopes suffered a punishing new setback Monday as authorities clamped down on his charitable foundation, while Hillary Clinton seized the offensive to brand him an unscrupulous businessman.

With just five weeks to go before the November 8 election, Trump is seeking to climb out of one of the darkest periods of his White House campaign as his vice presidential pick Mike Pence was set to go toe to toe against Democratic Senator Tim Kaine late yesterday for their only debate of the campaign.

Already weakened by damaging revelations about his taxes, the real estate billionaire was hit with an order by New York Attorney General Eric Schneiderman that the Donald J Trump foundation must "cease and desist from soliciting contributions" in New York.

The notice informed the charity that it had engaged in fundraising activities not permitted under the law because it had not been registered with the state authorities.

With Team Trump on the defensive after leaked documents suggested he may have paid no income tax for two decades, his Democratic rival rounded on him as a business bully who cares little for his fellow countrymen.

"While millions of American families, including mine and yours, were working hard paying our fair share, it seems he was contributing nothing to our nation. Imagine that," a fired up Clinton said in Toledo, Ohio.

"He has been 'dissing' America in this whole campaign," she charged, riding high on a surge in polling carried out after the bruising first presidential debate. The pair face off in their second showdown on Sunday.

Trump used an appearance before military veterans in Virginia to pound the former secretary of state once more for handling classified information via a "basement" private email server.

Farmville, a town of 8,000 nestled in the heart of central Virginia, was set to get a rare spell in the limelight last night when US vice presidential candidates Republican Mike Pence and Democrat Tim Kaine face off at Longwood University in their only debate of the general election campaign.

Pence, 57, the governor of Indiana, was expected to face tough questions about Trump's taxes and views on women, which have dominated the news for the past week.

Kaine, 58, a senator from Virginia, is a former governor of the state and was mayor of Richmond, the state capital. He will likely tout Clinton's experience and hammer away at Trump's policies as favoring the wealthy.