Donald Trump's speech at the World Economic Forum in Davos was mostly focused on the strength of the American economy and his desire to acquire Greenland, but the US president also vented about other world leaders.

Prime Minister Mark Carney of Canada "should be grateful", Trump said, a day after Carney delivered a blunt speech calling out "great powers" for weaponising their economic might.

The US president also took a jab at France's Emmanuel Macron, wearing sunglasses, and Switzerland's former president Karin Keller-Sutter, who, he said, rubbed him the wrong way.

Here's what Trump said about fellow leaders, and why the world is taking note.

'Canada lives because of the United States'

Calling out Canada's Prime Minister Carney by his first name, Trump said on Wednesday: "Canada lives because of the United States. Remember that, Mark, the next time you make your statements."

He added that Canada "gets a lot of freebies" from the US, and that "they should be grateful".

It is unclear whether Trump's comments were meant as a threat or a reminder, but Canadians are undoubtedly taking note.

Carney's address in Davos on Tuesday was widely lauded by politicians and pundits at home, with one senator describing it as the "most consequential" speech delivered by a Canadian prime minister since World War Two.

He did not name Trump directly, but did speak about "American hegemony" as he laid out how the world was undergoing "a rupture, not a transition".

At the end, he urged smaller powers to work together, adapt and reject coercion from "great powers".

Canada is still reeling from US tariffs imposed on key sectors like metals and cars.

It is also hoping for a renewal of USMCA, a North American free trade agreement that Trump sealed in his first term but is now under mandatory review.

A deal with the US is viewed as critical for Canada's economy, as it sells 75% of its products to its southern neighbour.

Asked about the possibility of repercussions on Wednesday, Canada's Trade Minister Maninder Sidhu said the US would "always be important for Canada", but that it was also looking elsewhere, like China and India, for opportunities.

French President Emmanuel Macron delivered his own speech at Davos yesterday.

He, like Carney, spoke of global instability and went on to call out the US for seeking to "weaken and subordinate Europe" by threatening tariffs on European allies and the UK over Greenland.

On Wednesday, Trump took aim at the pair of blue reflective aviator sunglasses Macron wore while giving his speech indoors.

"I watched him yesterday, with those beautiful sunglasses," Trump said. "What the hell happened?"

According to Reuters, the French leader wanted to protect his eyes because of a burst blood vessel, and French reports said he was dealing with an ongoing medical condition.

Last week, he appeared at a military event in southern France with a red eye and at one point donned a similar pair of sunglasses. He told troops his condition was "totally benign" and "completely insignificant".

Trump did not elaborate on the contents of Macron's speech, but he told White House reporters on Tuesday that he would not travel to Paris for a proposed G7 emergency meeting because he was doubtful of Macron's political future.

"He's a nice guy. I like Macron, but he's not going to be there very much longer," Trump said.

Trump criticises 'repetitive' former Swiss leader

The US president also expressed his views on the former Swiss president, Keller-Sutter, whom he referred to as "prime minister". Her term ended in December.

After he threatened last year to raise tariffs on goods from Switzerland to 30%, Trump recalled that she contacted him in a bid to avert the import taxes.

"She was very repetitive, she said 'no, no, no, you cannot do that, we're a small, small country,'" Trump said.

"She kept saying the same thing over and over," he added. "She just rubbed me the wrong way, I'll be honest with you."

After that call, Trump said he raised the duties to 39%.

It was an awkward moment for the Swiss delegation, which included Keller-Sutter and which had a meeting scheduled with him right after his speech,

Trump agreed to lower tariffs on Swiss products to 15% late last year amid pressure from major Swiss companies, including Rolex.

But the US president warned on Wednesday it could rise again.

"I reduced it because I don't want to hurt people," he said.

"I don't want to hurt them. And we brought it down to a lower level; it doesn't mean it's not going up."