Hundreds of wildfires burning across Canada are sending massive plumes of smoke into the United States, prompting air quality alerts, mandatory evacuations and health concerns for millions of people across the Northeast and Upper Midwest.

More than 830 active wildfires were reported across Canada, while more than a dozen additional fires continued to burn in northern Minnesota.

The fast-moving blazes have forced mandatory evacuations in several affected communities as firefighters battle to contain the flames.

In New York City, a thick orange haze shrouded the skyline on Wednesday, reducing visibility and signaling deteriorating air quality across the region.

Officials warned that unhealthy air conditions are expected to persist through Thursday.

Authorities also issued an Air Quality Health Advisory covering the entire state of New York, urging residents—particularly children, older adults and those with respiratory conditions—to limit prolonged outdoor activity.

Some of the largest and most intense fires are burning in west-central Ontario, where vast stretches of forest continue to fuel the blazes and generate enormous amounts of smoke.

Prevailing winds have carried the smoke southward into the United States, creating hazardous air quality for millions of residents from the Upper Midwest to the Northeast.

According to the U.S. Environmental Protection Agency’s AirNow monitoring system, air quality in New York City reached unhealthy levels on Wednesday afternoon.

Elevated pollution levels were also recorded across the Eastern Lake Ontario region, Central New York and parts of Western New York.

Meteorologists say smoke is expected to linger over much of the region through the end of the week, with changing wind patterns determining how long poor air quality persists.

Officials continue to advise residents to monitor local air quality forecasts and take appropriate precautions as wildfire smoke spreads across large portions of North America.