Wildfires in Canada have roared back to life, sending harmful smoke into the northern United States — an unwelcome reminder of last summer’s historic fire season that also repeatedly sent plumes of noxious haze southward.

Almost a year to the date from the explosive start to the 2023 fire season, hundreds of fires have erupted in Canada, including a dozen major and out-of-control blazes. At least 500,000 acres (200,000 hectares) of land have burned so far, much of it in recent days.

Canada's wildfire season has erupted as dozens of blazes burn in the country's western provinces, and smoke from those fires is choking the skies over the Upper Midwest early this week.

The Twin Cities of Minneapolis-St. Paul in Minnesota claimed the worst air quality in America on Monday after winds carried the smoke southeastward into the northern U.S.

Hazy skies were first seen Sunday over parts of northern Minnesota before spreading farther south into the Twin Cities overnight.

Central and northern Wisconsin are under an air quality advisory due to Canadian wildfire smoke, according to the National Weather Service in Sullivan.

In those portions of the state, people can see smoke in the sky, and in some areas, on ground level, said Mark Gehring, NWS meteorologist.

Visibilities are ranging from 4 to 7 miles in parts of west central and northern Wisconsin, as well as southern Minnesota, Gehring said.

Tens of millions of Americans are under air quality alerts Wednesday as a smoky haze from the ongoing Canadian wildfires envelops the skies of large portions of the Midwest and some areas of the East Coast, according to CNN.

Smoke from the wildfires burning in Canada is blowing south and causing dangerous air quality in New York state for the second time in a month.

On Wednesday at 12:40 p.m. EST, New York Governor Kathy Hochul tweeted that air quality health advisories were in effect for the entire state of New York.

Dense smoke from wildfires burning in Canada continued to migrate eastward Wednesday, swinging around a low-pressure area now moving offshore on the East Coast. In its wake, a channel of thick surface smoke draped across the Great Lakes and Ohio Valley, and increasingly over the Mid-Atlantic.

Millions of people in North America have been advised to wear N95 masks outdoors due to poor air quality levels sparked by intense wildfires in Canada.

New York will begin distributing free masks on Thursday. Canada has said that people should wear a mask if they are unable to remain indoors.

The smog is expected to spread beyond New York to other East Coast areas.

Officials warn that the dangerously smoky conditions are expected to persist into the weekend.