Trump, Clinton spending furiously

Defying his notorious stinginess, Donald Trump more than doubled his campaign spending last month.

Trump burned through roughly $US70 million ($A92 million) as his standing in polls and among fellow Republicans dropped.

Hillary Clinton, spent even more - almost $US83 million.

New reports filed with the Federal Election Commission outline their dramatically different approaches.

Trump, while putting more money than ever into advertising, spent a fraction of the roughly $US66 million Clinton poured into media buys.

Clinton's payroll topped 800 people, coming in as her second-highest expense of the month, about $US5.5 million.

Trump paid roughly 350 employees and consultants. He has outsourced most of his on-the-ground voter contact to the Republican Party.

The New York real estate mogul has bragged until recently about his low-cost campaign and dismissed the need for television ads and polling services. But in September, he paid $US23 million for commercials.

Perhaps a reflection of his newest campaign manager, pollster Kellyanne Conway, Trump appears to have a new interest in polling.

In August he paid Conway's The Polling Company $US130,000. Last month, he almost tripled his payment to her company, part of $US1.7 million in September expenditures to five different polling firms.

One of Clinton's expenditures causes a double-take.

Her campaign reimbursed employees who purchased $US260 worth of products from Trump International Hotel in New York.

That was for props - a tie, polo shirt and hat - in a Clinton campaign digital video highlighting that Trump doesn't make all of his products in America.

Indeed, the Clinton campaign line-item in the fundraising report reads: "Merchandise Not Made In America."

September was the best fundraising month for both candidates. Of the $US100 million Trump said he raised for his presidential bid and his Republican partners, about $US55 million went to his campaign.

Clinton's campaign said she raised $US154 million, and her September filing showed about $US74 million of that ended up in her campaign account.