Trump mocked the Europeans a day before heading to the World Economic Forum, where he will be the star of a dark, self-made drama over the fate of the autonomous Danish territory.

But leaders gathered at the Swiss ski resort have closed ranks against Trump's aggressive stance, with French President Emmanuel Macron vowing to stand up against "bullies" and the EU promising an "unflinching" response.

Asked how far he was prepared to go to acquire Greenland from Denmark, a fellow NATO member, Trump told reporters: "You'll find out."

Later as he left the White House, the president admitted he had "no idea" how the trip to Davos would pan out.

It got off to an inauspicious start when a "minor electrical issue" forced his presidential jet to turn back shortly after takeoff, and Trump and his entourage had to switch to another plane.

Trump's eagerly awaited speech at the annual gathering of the world's economic and political elite, which he is attending for the first time in six years, is scheduled for 2:30pm (1330 GMT).

But as the biggest rift opens between Washington and Europe in decades over his Greenland ambitions, Trump said he would have a number of meetings on the issue at Davos.

- 'Downward spiral' -

Trump insists mineral-rich Greenland is vital for US and NATO security against Russia and China as a melting Arctic opens up and the superpowers jostle for strategic advancement.

He has turned up the pressure by threatening tariffs of up to 25 percent on eight European countries for backing Denmark, prompting Europe to threaten countermeasures against the United States.

Trump dismissed European threats to fire a trade "bazooka" at the United States.

"Anything they do with us...all I have to do is meet it and it's going to go ricocheting backward," he said in an interview with News Nation.

"But we're not looking into that. We'll probably be able to work something out, possibly even during the next few days," he added.

At Davos on Tuesday, Macron, in sunglasses because of a burst blood vessel, warned against US attempts to "subordinate Europe", and blasted Trump's tariff threats as "unacceptable."

Macron was the subject of Trump's mockery as he publicly revealed a text message from the French leader proposing a G7 summit in Paris on Thursday on Greenland as well as Ukraine.

Trump later said he would not join any such meeting, while Macron clarified to AFP that no gathering was scheduled.

European Commission President Ursula von der Leyen meanwhile warned that Trump risked plunging US ties with the European Union into a "downward spiral".

And Canadian Prime Minister Mark Carney -- who has sought to reduce his own country's dependence on Washington since Trump called for it to become the 51st US state -- won a standing ovation at Davos for his stance.

"Canada stands firmly with Greenland and Denmark," Carney said.

In his Davos speech, the White House said Trump wanted to focus on the US economy amid a cost of living crisis that threatens his Republicans in the 2026 midterms.

But the US president's extraordinary assertion of US power on the world stage one year into his second term means Greenland will form the backdrop to the address.

- 'End of NATO' -

Greenland's prime minister said on Tuesday his tiny population of 57,000 must be prepared for military force.

Lithuania's President Gitanas Nauseda told AFP at Davos that any such move by the United States against a fellow ally "would be the end of NATO."

Trump said he had done "more for NATO than anyone" and questioned whether allies would help the United States -- despite the fact that Denmark was among those who did after the September 11, 2001 attacks.

On Thursday, meanwhile, Trump is set to formally announce the first charter of his so-called "Board of Peace," a body for resolving international conflicts with a $1 billion price tag for permanent membership.

The board was originally conceived to oversee the rebuilding of Gaza, but a draft of the charter seen by AFP does not appear to limit its role to the occupied Palestinian territory.