Out-of-control wildfires were raging on Thursday in the Canadian province of Ontario, sending dangerous smoke spewing into the United States where millions of people were exposed to the unhealthy air.

US states near the Canadian border including Minnesota, Wisconsin, Michigan and Illinois were particularly choked, as the Northeast including New York was also experiencing deteriorating air quality.

On Thursday afternoon, tracker IQAir listed Minneapolis, Detroit and Chicago as the top three most polluted cities in the world.

A thick, hazy cast hung over New York, where state authorities warned of fine particulate matter from the fires that would make the outdoors "unhealthy" for everyone across the New York metro area and Long Island.

Even worse air enveloped the central and western regions of the state.

Authorities encouraged New Yorkers to spend as little time outside as possible, with Mayor Zohran Mamdani warning of the "serious threat" of heavy heat and unsafe air.

Libraries and train stations were offering free masks, while hundreds of cooling centres were open across the city for those without access to air conditioning.

"This could become the most significant smoke event in New York City since 2023, and conditions will be closely monitored for any deterioration," the city's Department of Emergency Management said.

That year, the city's skies turned an eerie orange, with the air quality index reaching a dangerous 465.

In the Midwest, current index levels were already far beyond that figure, according to the US Environmental Protection Agency tracker.

Chicago along with Toledo, Ohio, and areas in Minnesota relatively close to the fires were well into the 700s on the air quality index, with much of the rest of the upper Midwest also experiencing AQI levels in the worst category of "hazardous."

The Michigan Department of Environment, Great Lakes, and Energy said it expected the dangerous conditions to continue through Friday, and that "our best model for smoke only predicts out to 48 hours."

"That model is currently showing improvements on Saturday, but it is likely that smoke will linger and recirculate for a while," the agency said.

In Canada, the latest data shows there are more than 130 active fires in northwestern Ontario, with at least 60 out of control.

Authorities there have formally requested additional assistance from the federal government, in particular seeking air support to evacuate remote communities.

The Ontario Provincial Police said 15 communities and their surrounding areas have been evacuated so far.

"More than 150 fire crews and nearly 50 firefighting aircraft are working around the clock to protect communities from the fires in northern Ontario," said the province's Premier Doug Ford on X.

So far, Canadian wildfires have scorched at least 1.9 million hectares this year, an area nearly the size of Slovenia.

That damage remains far off the pace of 2023, Canada's worst wildfire season on record, when nearly 18 million hectares burned in the country. (AFP)



Edited by Cecil Wong