Thousands of people have been told to leave more than a million acres of wilderness as wildfires spread.

Rangers in the US state of Minnesota are trying to evacuate up to 10,000 visitors from the Boundary Waters Canoe Area Wilderness after 17 fires were sparked there by lightning.

The wilderness spans a vast 1.1 million acres and is almost the size of Delaware, spokesperson Joy VanDrie told NBC News, Sky's US partner.

She called getting out an "arduous job" as rangers and campers had to canoe for hours or even carry their boats over land.

No injuries or deaths have been reported and rangers believed around 90% of people had left by Wednesday.

Across the nearby Canadian border, some 835 wildfires are active, mostly in the central provinces of Manitoba, Saskatchewan and Ontario, with 112 of them burning out of control, according to the country's government.

So far, 1.9 million hectares (4.7 million acres) have burned.

Smoke has been drifting from northwestern Ontario across parts of the northeastern US, turning skies dark and reducing air quality to dangerous levels.

Canadian environmental officials warned people to limit outdoor activities after Toronto's air quality was ranked worst among the world's major cities on Wednesday.

Environment Canada gave the city an Air Quality Health Index reading of 10+, classified as "very high risk," with hazardous conditions forecast to last until Thursday night.

Wildfires are raging through sparsely populated areas hundreds of miles from ​Toronto, sending smoke over a wide area, although they are not directly threatening cities.

A train crew in northern Ontario filmed themselves surrounded by flames before being safely evacuated.

Two small groups of children were also rescued after becoming trapped by fires while camping in the Canadian wilderness, the Minnesota Star Tribune reported.

"Both groups have been rescued and are ‌on their way back home to safety," Minnesota Governor Tim Walz said on X.

Meanwhile, Minnesota and New York residents have also been warned about unhealthy air conditions amid unusually hot summer temperatures.

It comes as New Jersey gears up to host the World Cup final on Sunday.

(c) Sky News 2026: Wildfires force thousands to evacuate as skies darken over US and Canadian cities