WASHINGTON (AFP) - Republican Donald Trump said Monday he will slash taxes, block onerous financial regulations and unleash the energy sector as he pledged to "jump-start America" with a new economic plan if he is elected president.

The brash billionaire unveiled his plan during a speech in economically depressed Detroit as he tries to reset his campaign and focus on policies that draw a sharp contrast with his Democratic White House rival Hillary Clinton.

"We are in a competition with the world, and I want America to win," Trump told the Detroit Economic Club, as he highlighted "disastrous" policies that he said have snuffed out US jobs in the nearly eight years of Barack Obama's presidency.

"I want to jump-start America. It can be done, and it won't even be that hard," he said to applause.

Trump laid out a series of policies he said are aimed at revitalizing a limping economic engine, including a sharp reduction of corporate tax to 15 per cent from 35 per cent, something he floated back in September as a way to lure back US corporations that relocated abroad.

He would also set a 10 per cent tax on the "trillions of dollars from American businesses that is now parked overseas" and gets repatriated into the United States.

Personal taxes would drop too, with seven tax brackets compressed to just three. The highest income tax rate would be 33 per cent, compared with today's top rate of 39.6 per cent.

Trump said he wants to "cut regulations massively," a move he said would lift the "anchor" weighing down small businesses, something Republicans have sought for years during Obama's tenure.

Calling for such a moratorium could help the New York real estate tycoon win support from small business owners who have argued they have been over-regulated under Obama's presidency.

Trump also proposed repealing the estate tax, the controversial levy on the estates of the deceased valued at above US$5.45 million.

"American workers have paid taxes their whole lives, and they should not be taxed again at death - it's just plain wrong," Trump said.

He also announced a plan to allow parents to "fully deduct" childcare costs from their taxes.

The speech was interrupted more than a dozen times by protesters, who were escorted out by security.

As Trump faces several polls showing him trailing Clinton, and as he pivots away from recent controversy about his campaign, he portrayed Clinton as the "nominee from yesterday".

"There will be no change under Hillary Clinton - only four more years of Obama," he warned. "But we are going to look boldly into the future."

Clinton, he said, offers more of the same: "more taxes, more regulations, more bureaucrats, more restrictions on American energy".

The Clinton camp, in an effort to get out ahead of Trump's economic plan, released a video savaging "the dangers of Trumponomics".

Her campaign has cited a study by Mark Zandi, a former economic advisor to Republican Senator John McCain, which predicted that under Trump's plan, the economy would shed 3.4 million jobs and tumble into recession.

Since officially winning the Democratic nomination late last month, Clinton has spent several days attacking Trump on the economy.

She has also ventured into America's so-called "Rust Belt" seeking to win over white working-class voters in areas that have suffered factory closures.

The nation's unemployment rate stood at 4.9 per cent in July, a substantial decline from the peak of about 10 percent in October 2009 after a major recession, according to federal statistics.

But Trump insisted the economy was lagging badly and that letting an insider like Clinton guide the economic ship would only exacerbate the problem.

"We can't fix a rigged system by relying on the people who rigged it in the first place," Trump warned.

"A Trump administration will end this war on the American worker," he said, noting in particular that Obama's "anti-energy regulations" have destroyed millions of jobs.

Trump's plan to revitalize the energy industry, including coal, would "open a new chapter in American prosperity", he said.

Trump renewed his opposition to the proposed Trans-Pacific Partnership trade pact backed by the Obama administration, insisting Washington will withdraw from the deal.

"Americanism, not globalism, will be our new credo," he said.