Smoke from wildfires burning in Quebec blankets Ontario, northeastern U.S.

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The scent of campfire hung in the air as smoke from wildfires raging in Quebec and other provinces blanketed some of the biggest cities in Ontario and the northeastern U.S., making the air quality in those areas among the worst in the world.

On national Clean Air Day in Canada, a grey cloak of smoke was visible in the most populated corridor in the country, including the Greater Toronto Area and the Ottawa region. Meanwhile, an eerie orange haze blotted out the sun in cities further south, such as New York.

In Ottawa and York Region, north of Toronto, smoke led to school boards cancelling outdoor recesses and sports leagues. In New York, some flights were delayed or cancelled because of low visibility while Major League Baseball’s Yankees had their game postponed.

Officials in both countries spoke about the unprecedented intensity of this year’s fire season, which has affected millions of people, and highlighted how critical it is to take action on climate change.

The number of fires and the vast swath that has been torched has already reached a record high in Canada, with the hottest months of the year still to come. More than half of the 414 fires burning from coast to coast are determined to be out of control, displacing 20,183 people from their homes, said Emergency Preparedness Minister Bill Blair during a news conference.

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Prime Minister Justin Trudeau, at the same media event on Parliament Hill, said more frequent and intense weather events, such as fires, will impose high costs on communities, families and the country as a whole, and the path ahead needs to include continued efforts to fight climate change.

“In coming years, we will have to reflect seriously on how we can equip ourselves to deal with this new reality,” said Mr. Trudeau. He added that the federal government is discussing the creation of a national disaster-response agency so that Canada can better “predict, protect and act” in extreme-weather situations.

Also on Wednesday, the White House said President Joe Biden has been receiving regular briefings on the wildfires in Canada since last week, and that the U.S. has sent help north of the border to help fight the blazes. Fire crews from Australia, New Zealand and South Africa are also on the ground, with others soon coming from France to help Quebec.

Mr. Biden called Mr. Trudeau Wednesday to “offer additional support” in fighting the fires, the White House said in a summary of the call. The President ordered “all available federal firefighting assets” to be scrambled to Canada. Earlier in the day, White House press secretary Karine Jean-Pierre said the U.S. had already deployed 600 firefighters and some water bombers to Canada.

The summary said the two leaders also discussed fire prevention and dealing with the health effects of the fires.

Washington, hundreds of kilometres south of the fires, awoke Wednesday to smoke clouding the sky and enveloping its monuments, prompting some commuters to don KN95 masks for some protection. Local officials have issued a “code-red” alert as the city registered an air quality index score of 188, roughly on par with Delhi and worse than some perennial smog hot spots such as Jakarta and Shanghai.

By afternoon, the air quality in New York was the worst of any major city in the world.

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Congressman Dan Goldman, who represents a New York district, said the fires were another reminder of the need to fight climate change, which has made the forests more vulnerable to conflagration. He said New York and Washington have, in decades past, not been hit by such intense smoke from fires so far away.

“This is no longer about the future of our planet. This is about the present,” said Mr. Goldman.

The congressman said he hopes being directly affected by climate change will spur more congressional action. Last year’s Inflation Reduction Act put money into green-energy subsidies, but Mr. Goldman argued that the country had to do more, including overcoming climate denial by some members of Congress.

In contrast, Ontario Premier Doug Ford would not link the blazes to human-caused climate change after facing repeated questions from NDP Opposition Leader Marit Stiles. He said lightning and campfires were to blame and accused Ms. Stiles of “politicizing” the wildfires. “They happen every single year,” said Mr. Ford.

Ontario’s Minister of Natural Resources and Forestry, Graydon Smith, later told reporters that “climate change is real and happening” and that the government is working to reduce emissions by funding the transition to electric furnaces in the steel industry and with carbon-capture initiatives.

Officials in Quebec said nearly two-thirds of the 150 wildfires currently burning in the province are deemed out of control. More than 457,000 hectares have burned so far this season, the most since the province started keeping records. So far, about 11,400 people have been forced from their homes and thousands more were expected to be added to the evacuee list later on Wednesday.

Northern Quebec and the western Abitibi regions are the most troublesome areas but rainfall needed to stifle the blazes is not in the immediate forecast.

Premier François Legault said Quebec is in negotiations with the U.S., Portugal, Spain and Mexico for additional resources to boost the number of firefighters on the ground from 520 to 1,200 in the coming weeks. About 150 members of the Canadian Armed Forces are already assisting.

Active fires are burning in a number of other provinces and territories, including Alberta, British Columbia, Nova Scotia and Saskatchewan. Nearly 2,300 wildfires have occurred in Canada this season, scorching 3.8 million hectares.

In Nova Scotia, the largest of its four active wildfires, covering 234 square kilometres in the southwest, is being held. This means the blaze is not expected to grow if conditions remain the same. But Tory Rushton, the province’s Minister of Natural Resources and Renewables, said, “I want to be clear: It is still not under control.” A callout for volunteer firefighters has been initiated.

With reports from Ian Bailey in Ottawa, Adrian Morrow in Washington, Jeff Gray in Toronto, Lindsay Jones in Halifax and The Canadian Press