President-elect Donald Trump came under fire Thursday for picking a global warming skeptic as his new environment chief, ahead of a visit to the American Midwest that helped him win the White House.

The 70-year-old property tycoon, who has never previously held elective office, has spent the majority of his time since his November 8 defeat of Hillary Clinton sequestered in his New York headquarters building his cabinet.

His team says more than 50 percent of those positions have now been filled, with 43 days to go before the Republican will be sworn in as the 45th president of the United States, the oldest man ever inaugurated into the office.

He reportedly will nominate fast food executive Andy Puzder to be his labor secretary.

The transition team says his pace of appointments outstrips that of any modern US administration, but opponents hounded Trump for nominating an ally of the fossil fuel industry to head the Environmental Protection Agency (EPA).

Trump's choice of Oklahoma's attorney general Scott Pruitt has outraged many Democrats and environmental experts who fear that he will reverse outgoing Democratic President Barack Obama's efforts to combat climate change.

In announcing the nomination of Pruitt -- who will need Senate approval -- Trump complained that "for too long," the EPA had spent "taxpayer dollars on an out-of-control anti-energy agenda that has destroyed millions of jobs."

Pruitt "will reverse this trend and restore the EPA's essential mission of keeping our air and our water clean and safe," the president-elect said.

The EPA chief can wield strong influence on US actions to combat climate change: the agency both determines what international commitments the country is able to make, and implements them.

- 'Outer extreme edge' -

Opponents scoffed at Trump's suggestion that Pruitt will be a safe steward of the environment, pointing out he has spent much of his time battling the very agency he is now tapped to lead.

"Scott Pruitt has spent the past several years fighting tooth and nail to help polluters erase or circumvent the critical environmental protections our nation has put in place," said Steny Hoyer, the number two Democrat in the House of Representatives.

"There is nothing good about this," Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia Law School, told AFP.

"Pruitt is a known conspirator with the fossil fuel industry and I mean that in a literal sense," he said, pointing to the Oklahoman's 2014 efforts with oil companies to battle EPA regulations.

Ken Kimmell, president of the Union of Concerned Scientists, described Pruitt as someone "on the outer extreme edge, and putting him in charge of EPA could really have devastating consequences."

While campaigning, Trump said Obama's environmental regulations were hamstringing US businesses and vowed to roll back regulations and slash corporate taxes in an effort to drive job creation and business growth.

But he does seem to be courting opinion from the other side of the political aisle, meeting this week with former Democratic vice president-turned-climate campaigner Al Gore and also reportedly with actor Leonardo DiCaprio, who is an active environmentalist.

While his cabinet nominations offer clues as to Trump's projected policies, observers worldwide remain on tenterhooks over how exactly he will manage the climate, national security, trade, immigration and foreign policy.

- Stops in Ohio and Iowa -

All eyes remain fixed on his pending announcement of his candidate for secretary of state, with Exxon chief executive Rex Tillerson and former Ford boss Alan Mulally reportedly late additions being considered.

But Trump will take a break from cabinet interviews on Thursday when he heads to Ohio to meet the survivors and first responders of last week's car-and-knife campus attack before headlining a victory rally in swing state Iowa.

Trump, who during the campaign called for Muslims to be banned from entering the United States, tweeted after the November 28 attack that the assailant, who migrated from Somalia, should not have been in the country.

Abdul Razak Ali Artan was shot and killed by police after driving into a crowd and then slashing several people with a knife. Officials said 11 people were treated for injuries.

Investigations into the motive are ongoing. Artan reportedly referred to Al-Qaeda teachings on Facebook. A jihadist-linked news agency called him a "soldier" of the so-called Islamic State group fighting in Iraq and Syria.

It will be Trump's second visit to Ohio since winning the election, having kicked off his victory tour in Cincinnati last week. The Rust Belt state, won by Trump, voted for a Republican to take the White House for the first time since 2004.

From there, Trump will travel to Des Moines to headline a "thank you" rally with Vice President-elect Mike Pence, following similar previous events in Cincinnati and North Carolina.

Also in attendance will be Iowa Governor Terry Branstad, a long-time Trump supporter and long-time personal friend of Chinese President Xi Jinping who has been nominated to serve as ambassador to Beijing.