Toronto recorded the worst air quality among major cities worldwide on Wednesday as thick wildfire smoke from northwestern Ontario blanketed the city and drifted into the northeastern United States, triggering widespread health warnings, disrupting public events and raising fresh concerns over the growing impact of climate change.

Authorities in both Canada and the United States urged residents to limit outdoor activities as hazardous air conditions spread across the region, while India ordered its seafarers to avoid voyages through the Strait of Hormuz due to separate escalating security concerns in the Middle East.

Environment Canada reported an Air Quality Health Index (AQHI) reading of 10+, classified as “very high risk,” for Toronto, warning that dangerous air quality conditions could persist through Thursday night.

The smoke originated from hundreds of wildfires burning across sparsely populated areas of northwestern Ontario and other central Canadian provinces. Although the fires were not directly threatening major cities, smoke from the blazes spread across vast areas, significantly reducing air quality.

According to Swiss air quality technology company IQAir, Toronto ranked as the city with the worst air quality globally on Wednesday, surpassing Kinshasa and Delhi, while New York City ranked fifth.

The deteriorating air conditions also reached New York and neighbouring states ahead of Sunday’s FIFA World Cup final in New Jersey.

Local authorities issued air quality alerts after pollution levels reached unhealthy levels, advising residents to reduce strenuous outdoor activities and take additional precautions if spending time outside.

The US National Weather Service warned that the smoke could remain over the region through the end of the week.

“We probably haven’t seen the worst of it yet for New York City. We probably haven’t seen the worst of it yet for the Great Lakes and upstate and New England yet either,” said Dan Westervelt, Lamont associate research professor at Columbia University.

The worsening air quality forced Toronto officials to cancel the FIFA Fan Festival and the England-Argentina World Cup watch party scheduled for Nathan Phillips Square.

More than 80,000 spectators are expected to attend the World Cup final at the open-air stadium in New Jersey on Sunday, while another 50,000 fans are expected to gather at Central Park in Manhattan, where skies had already turned visibly hazy.

New York Governor Kathy Hochul warned residents that smoke and haze from the Canadian wildfires were creating unhealthy air conditions across the state.

She encouraged vulnerable residents, particularly those with existing health conditions, to exercise caution and minimise outdoor exposure.

Meanwhile, the wildfires also disrupted transportation and outdoor recreation in northern Ontario.

A widely shared video on social media showed a Canadian National freight train surrounded by flames near Armstrong, Ontario.

Canadian National confirmed that rail operations near Armstrong, more than 500 kilometres north of Toronto, had been suspended as a precaution after employees and residents were evacuated from the area on Monday night.

The fires also stranded two groups of children from Minnesota who were participating in a YMCA wilderness camping trip in Canada.

According to the Minnesota Star Tribune, one group was evacuated by helicopter with assistance from the Canadian military before both groups were safely rescued.

“Both groups have been rescued and are on their way back home to safety,”

Minnesota Governor Tim Walz said on X.

The Government of Canada said the 2026 wildfire season had started more slowly than the devastating seasons of 2023 and 2025 but warned that above-average temperatures were expected to increase wildfire risks across the country.

Government data showed that 835 active wildfires were burning across Canada on Wednesday, with 112 classified as out of control. About 1.9 million hectares (4.7 million acres) have already been destroyed, with most of the fires concentrated in Manitoba, Saskatchewan and Ontario.

Experts warned that severe smoke events are likely to become increasingly common as climate change intensifies.

Professor Greg Evans of the University of Toronto said the city was experiencing the combined effects of extreme heat and wildfire smoke. “I expect that this will occur more frequently over the coming decades so cities and residents need to prepare for this in the future.”

Toronto resident Paula Oreskovich said the thick haze and smell of smoke were immediately noticeable when she stepped outside on Wednesday morning.

“I think you have to be silly if you’re not going to be concerned about climate change. It’s definitely here, it’s definitely happening, and it’s happening globally.” (Arise News)