Republican White House frontrunner Donald Trump said Tuesday he will start spending millions of dollars in hard-hitting campaign advertising in the run-up to the first votes in the 2016 presidential race.

Trump, a billionaire real estate tycoon who is self-funding his campaign, has spent virtually no money in political television ads. But that is changing.

‘I'll be spending a minimum of $2 million a week, and perhaps substantially more than that,’ he told reporters on his campaign plane.

Trump has been leading nationally in all polls for months, and his bombastic and provocative style has allowed him to dominate the media spotlight, without spending any of the $35 million he said he had expected to use on ads by January 1.

‘I'm proud of the fact I can spend the least,’ he said.

But ‘honestly, I don't want to take any chances.’

Iowa votes first in the nation in the nomination race, with its caucuses on February 1. New Hampshire votes eight days later, followed by South Carolina and then Nevada.

Trump said he expects to unveil ‘very substantial’ ads in Iowa, New Hampshire and South Carolina.

The spots will focus on border issues, trade, the fight against Islamic State extremists and national security.

He signalled he would not hesitate to unleash attack ads on rivals if any of them assails him directly.

‘I will spend a lot of money against the people that go after me,’ he warned.

And he took a swipe at Republican rival Jeb Bush, who Trump said has gone ‘nowhere’ despite the former Florida governor's struggling campaign and pro-Bush organizations reportedly spending $59 million since launching his presidential run.