Heavy smoke from hundreds of Canadian fires enveloped a swath of the US from the Midwest to the Northeast on Thursday and Friday, prompting warnings to residents to stay indoors.

Trump, who has a combative relationship with Canadian Prime Minister Mark Carney, said he would be calling the Canadian leader to find out what he planned to do about the "totally unacceptable" situation.

"We are holding Canada responsible for the fact that they are not properly maintaining their Forests [...] and the United States is being unnecessarily invaded by filthy, polluted, and unhealthy air," he said in a Truth Social post.

"This is Willful Negligence, and becoming a yearly occurrence, costing the United States Billions of Dollars, which cost of this pollution must of necessity be added to the TARIFFS Canada is currently paying."

Canada's minister of emergency management and community resilience, Eleanor Olszewski, said the government has invested C$12 billion (US$8.56 billion) in forest sustainability and fire prevention since 2020 as the country faces increasingly drier, warmer weather.

She also cited a long history of US-Canadian partnership in fighting wildfires on both sides of their border.

"At this time, our first priority is protecting Canadians and keeping communities safe," Olszewski said in a statement.

Climate experts say rising temperatures have led to drier timber and more wildfires in recent years in Canada, home to some of the world's largest forest landscapes.

"As our climate warms, we're seeing [...] more extreme weather, and we're going to see more fire," said Mike Flannigan, a professor of wildland fire at Thompson Rivers University in British Columbia.

Shortly after taking office in 2025, Trump imposed tariffs on several key imports from Canada.

Carney's office did not immediately respond to a request for comment on Trump's remarks. Carney said on Thursday the United States could do more to combat climate change that is leading to more prolonged drought and rising temperatures around the world.

The two men are likely to meet at the FIFA World Cup final in New Jersey on Sunday.

Many blazes this year are in the giant province of Ontario and are concentrated in the remote and sparsely populated northwest, where the only mode of transport is via air. So far, 2,630 square kilometers have burned, compared with 2,428 sq km at the same time last year. Thousands of people have been evacuated.

'Nothing remaining'

The Namaygoosisagagun First Nation, also known as Collins First Nation, in northwestern Ontario went up in flames, forcing residents to evacuate by boat and seek shelter in Thunder Bay, Matthew Hoppe, the community's incident commander, told Reuters.

"There was nothing remaining. So as you can imagine, the membership is totally distraught, upset, overwhelmed, lost," Hoppe said.

Thunder Bay, a city of about 110,000 people on the northern shore of Lake Superior more than 1,300 km northwest of Toronto, is at full capacity from sheltering wildfire evacuees from across northwestern Ontario, Mayor Ken Boshcoff told Reuters.

Ontario Premier Doug Ford on Friday said the province would buy 11 new aircraft to help counter the fast-spreading wildfires and pushed back against US politicians who have criticized the campaign as inadequate.

The US is also experiencing an above-average fire year, with 14,973 sq km burned to date in 2026 compared with a 10-year average of 10,926, according to the National Interagency Fire Center.

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