July 16 (UPI) — Thick smoke from Canadian wildfires poured into northeastern quarter of the United States on Thursday after similarly darkening skies across and prompting health warnings across much of the Great Lakes region.

Dangerous levels of smoke were noted across Canada and the northeastern and midwestern United States, sparking memories of the historically severe wildfire smoke outbreak in 2023.

Entire states including New York, New Jersey, Connecticut, Delaware, Massachusetts, Michigan, New Hampshire, Ohio, Pennsylvania, Rhode Island and Wisconsin were under air quality alerts.

By early Thursday, Minneapolis, Duluth, Minn., and Detroit were among the most heavily impacted areas of the country.

Very heavy smoke from large wildfires in northern Minnesota and northwestern Ontario spread over Minnesota from late Wednesday into Thursday morning, the Minnesota Pollution Control Agency reported.

Hourly observations of smoke concentrations broke records for the Twin Cities on both days, the agency said.

In Detroit, businesses and attractions closed due to poor air quality.

A planned concert by rocker John Mellencamp at Pine Knob Music Theatre in Clarkston, Mich., was canceled while some workers inside Ford Motor’s Michigan Assembly plant in Wayne, Mich., were hospitalized amid the smoky haze and intense heat, the Detroit Free Press reported.

Michigan’s statewide air quality alert was extended through Friday before cooler weather was expected to move the smoky pall out of the Great Lakes region.

In Chicago, the city closed all of its public beaches and outdoor pools, while Milwaukee recorded the worst air quality in its history — a record-breaking Air Quality Index measured at over 600, according to the Milwaukee Journal.

Further east, smoke from the Canadian wildfires enveloped New York City, prompting Mayor Zohran Mamdani to urge residents to “take precautions to stay cool and out of harm’s way” while dealing with both the smoke and high temperatures.

“In our city, we pride ourselves on being resilient,” the mayor told reporters early Thursday. “Today is not a day to say, ‘In spite of the air quality, I’m going to do everything I was going to do yesterday.’ This is very serious. We are reaching into a level of air quality that is dangerous for every single New Yorker.”