NEW YORK (AP) — Heavy, pungent smoke from Canadian wildfires darkened skies in the U.S. on Thursday, from the Great Lakes to parts of the East Coast, reducing visibility for commuters and prompting warnings about air quality that made outdoor activities dangerous.

Detroit’s air quality was among the worst in the world for major cities, as a lingering high pressure system trapped smoke from dozens of fires in Canada and northern Minnesota and winds from the northwest blew it into Michigan, said Steven Freitag, a National Weather Service meteorologist in Pontiac, Michigan.

“Sure enough, it arrived in force here and it’s really pretty extreme levels,” said Freitag, who noted that visibility in some areas was reduced to a half mile.

Some other cities across the Great Lakes states also registered air quality ranging from unhealthy to hazardous. Fine particles in smoke are especially dangerous for children and people with health conditions such as asthma and heart disease.

In the New York City area, a thick, gloomy haze tinged the morning sky in orange-and-yellow, reducing visibility so dramatically that it partly obscured Manhattan’s prominent skyline.

City officials opened cooling centers as health officials urged New Yorkers to limit strenuous and prolonged outdoor activities and to stick to air-conditioned spaces as much as possible.

State officials distributed tens of thousands of face masks designed to filter out 95% of tiny airborne particles, including dust and smog, at the city’s Penn Station and Grand Central transit hubs and other major locations.

Mayor Zohran Mamdani said public schools, parks and other city agencies were adjusting programming, moving activities indoors, rescheduling events and adjusting operations as air quality was expected to worsen as the day progressed.

The state Department of Environmental Conservation issued a statewide air quality health advisory.

The agency said there was a potential for temporary spikes of “very unhealthy” air quality from Buffalo in the state’s western corner to Rochester by Lake Ontario, Syracuse in the central region, down to the greater New York City area.