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Authorities in New York, Toronto and Ottawa on Tuesday warned residents of the health risks of air polluted by the smoke of unprecedented wildfires in early summer in eastern Canada.
An unusually early and intense start to the wildfire season is leading Canada into the worst year as warm and dry conditions are forecast to last for months.
Fires have occurred in nearly all 10 provinces and territories of Canada, with Quebec being most affected by numerous lightning fires.
The New York State Department of Environmental Protection has issued health recommendations for some counties, including New York, the Bronx and Queens.
Canada Expects More Months of Forest Fires
The state recommends residents consider limiting heavy outdoor physical activity to reduce the risk of adverse health effects.
The Canadian capital, Ottawa, which is adjacent to Quebec, has been covered in smog since Tuesday morning, with air quality in category 10+, the worst level in Environment Canada's Air Quality Health Index, indicating a "very high risk."
"Pillars of smoke from local forest fires as well as forest fires in Quebec have led to degraded air quality," Ottawa Air Quality Warning said.
The air over Toronto was also polluted and adverse conditions may persist for most of this week, the government's meteorological agency said.
Smoke from forest fires can harm health even at low concentrations, and people with lung or heart disease, as well as the elderly, children and pregnant women, are at higher health risk than smoke from forest fires, environmental authorities said.
Canada's Foreign Minister Melanie Jolie thanked the United States, Mexico, South Africa and France on Tuesday for sending firefighters to help.
Wildfires are common in Canada's western provinces, but this year the flames flared quickly in eastern Canada, forcing the evacuation of residents and sending the army.
About 3.3 million hectares have already been burned - about 13 times the 10-year average - and more than 120,000 people have been at least temporarily forced to flee their homes.
"I want to stress that people should continue to listen to local authorities on how to stay safe, including in places like Ottawa that are affected by the smoke of forest fires," Prime Minister Justin Trudeau told reporters in Ottawa.