NEW YORK — Smoke from Canadian wildfires poured into the U.S. East Coast and Midwest on Wednesday, covering the capitals of both nations in an unhealthy haze, holding up flights at major airports and prompting people to fish out pandemic-era face masks.

While Canadian officials asked other countries for additional help fighting more than 400 blazes nationwide that already have displaced 20,000 people, air quality with what the U.S. rates as hazardous levels of pollution extended into central New York and northeastern Pennsylvania. Massive tongues of unhealthy air extended as far as North Carolina and Indiana, affecting millions of people.

“I can taste the air,” Dr. Ken Strumpf said in a Facebook post from Syracuse, New York, which was enveloped in an amber pall. The smoke, he later said by phone, even made him a bit dizzy.

In Baltimore, where officials urged residents to stay indoors, Debbie Funk sported a blue surgical mask as she and husband, Jack Hughes, took their daily walk around Fort McHenry, a national monument overlooking the Patapsco River. The air hung thick over the water, obscuring the horizon as distant ships pushed slowly through the haze.

“I walked outside this morning, and it was like a waft of smoke,” said Funk, who said the couple planned to stay inside later Wednesday.

Canadian officials say this is shaping up to be the nation’s worst wildfire season ever. It started early on drier-than-usual ground and accelerated very quickly, exhausting firefighting resources across the country, fire and environmental officials said.

Smoke from the blazes in various parts of the country has been lapping into the U.S. since last month but intensified with a recent spate of fires in Quebec, where about 100 were considered out of control Wednesday.

“The smoke was insane” on Tuesday, said Zachary Kamel, 36, of Montreal. “I had to close my window because the fresh air just smelled like campfire.”

Quebec Premier François Legault said the province has the capacity to fight about 40 fires at the moment — and the usual reinforcements from other provinces have been strained by conflagrations in Nova Scotia and elsewhere.

Canadian Interagency Forest Fire Centre spokesperson Jennifer Kamau said more than 950 firefighters and other personnel have already arrived from the U.S., Australia, New Zealand and South Africa, and more will be arriving soon.

In Washington, White House press secretary Karine Jean-Pierre said that President Joe Biden has sent more than 600 firefighters and equipment to Canada and that his administration has contacted some U.S. governors and local officials about providing assistance.

The largest town in Northern Quebec — Chibougamau, population about 7,500 — was evacuated Tuesday, and Legault said the roughly 4,000 residents of the northern Cree town Mistissini would likely have to leave Wednesday.

Eastern Quebec got some rain Wednesday, but Montreal-based Environment Canada meteorologist Simon Legault said no significant rain is expected for days in the remote areas of central Quebec where the wildfires are more intense.