US Republican presidential nominee Donald Trump has said he is taking the gloves off in his battle against Democrat Hillary Clinton in the race for the White House, after taking a scorching from speakers at the Democratic National Convention.

Key points: Trump kicks back at Democrats after convention grilling

Trump kicks back at Democrats after convention grilling Clinton ad slams Trump for comments against disabled people and women

Clinton ad slams Trump for comments against disabled people and women Trump says he is 'starting to agree' with calls for Clinton to be locked up

Mr Trump wrapped up a five-day, seven-state campaign swing in Colorado on Friday, where for a fifth straight day his supporters chanted "lock her up" whenever he brought up Mrs Clinton's name.

Mr Trump supporters say Mrs Clinton deserves to be prosecuted for her handling of US foreign policy as President Barack Obama's first-term secretary of state and for her use of a private email server while in that office.

All week Mr Trump has sought to tamp down the chants by stressing that his main goal is to simply beat Mrs Clinton in the November 8 presidential election.

But as the crowd chanted the slogan in Colorado Springs, Mr Trump finally relented.

"I'm starting to agree with you, frankly," he said.

"No more Mr Nice Guy."

In Denver later, he changed his tune when he heard the chant.

"I'll tell you what I'd rather do, honestly, is just beat her on November 8 at the polls," he said.

"She would be a disaster."

'I didn't know he was disabled': Trump

Mr Trump was a punching bag at the Democratic convention in Philadelphia, which wrapped up on Thursday night, as speaker after speaker — including some Republicans — said he lacked the temperament to be president.

Mrs Clinton herself said in her acceptance speech that the election represented a "moment of reckoning" for the country.

In Colorado Springs, Mr Trump got sidetracked by a couple of disputes from last year as he tried to rebut a Clinton campaign ad.

The ad uses video clip from Mr Trump's attack on Fox News anchor Megyn Kelly in protest against her questioning of him at a debate of Republican presidential contenders last August when he said afterward that blood was "coming out of her eyes, coming out of her wherever".

"I was talking about her nose," Mr Trump said in Colorado Springs.

"I wanted to get back on the issue of taxes [at the debate]."

Mr Trump also brought up the case of disabled New York Times reporter Serge Kovaleski, whom Mr Trump seemed to mock publicly in video used by the Clinton ad.

Mr Trump said he was depicting the reporter grovelling to him.

"I didn't know he was disabled. I didn't know it at all. I had no idea," he said.

Reuters