Air quality in Canada’s largest city was at times the worst in the world on Wednesday, as wildfires across Ontario sent smoke drifting into New York City and beyond.

Air quality in Canada’s largest city was at times the worst in the world on Wednesday, as wildfires across Ontario sent smoke drifting into New York City and beyond. Wildfires have swept across Ontario, prompting dozens of communities to evacuate and sending acrid smoke to New York City and across the U.S. northeast. Parts of Canada, including its most populous city, Toronto, woke Wednesday to a hazy, orange sky, the air smelling strongly of wood smoke. Air quality readings for the city triggered a warning from Environment Canada, a federal department, about the health risks of spending time outdoors. “We’re really being fumigated,” said Brian Proctor, a meteorologist at Environment Canada, adding that people across New York state can also anticipate worse air quality measures through the day tomorrow as the smoke makes its way southeast. “In general terms, expect it to get worse before it’s going to get better in the next 36 hours,” said Mr. Proctor. At least six rural and First Nations communities have been evacuated around Thunder Bay, Ontario, a city on Lake Superior about an hour’s drive from the Minnesota border. Members of Namaygoosisagagun First Nation, a community of about 40 residents, evacuated their homes by boat. “An entire first nations community has been erased because of this disaster,” Sol Mamakwa, an Indigenous member of provincial parliament, said in a statement, offering his support to residents of the community, also known as Collins First Nation. Three trains transporting flammable cargo were threatened by flames along the tracks and held at a safer location, the Ontario Provincial Police said.