'Trees vanished in seconds': Canadian wildfire smoke prompts air quality alerts in US

Detroit and Minneapolis rank among the top major cities with poor air quality.

Air quality alerts are in place on Thursday across at least 17 states, from Minnesota to New Hampshire to Virginia, as dangerous smoke continues to waft into the U.S. from Canadian wildfires, including more than 100 blazes burning out of control.

Smoke from at least 850 active wildfires in Canada is traveling more than a thousand miles to reach U.S. locations including New York City. At least another nine large fires are burning in northern Minnesota.

On Thursday morning, Detroit, Michigan, had the worst measured air quality in the world among major cities, according to the air quality monitoring website IQAir. Detroit reached an air quality index, or AQI, of nearly 570 as of early Thursday afternoon.

IQAir rates the most dangerous air quality index, described as "hazardous," as 301 or above.

Minneapolis, Chicago and Toronto, Ontario, ranked second, third and fourth on IQAir's AQI scale on Thursday afternoon for the worst air quality on the planet. Toronto is more than 1,100 miles from where 180 wildfires are burning in sparsely populated areas of Ontario province.

Meanwhile, all of New York State, including New York City, and parts of New Jersey are under an Air Quality Advisory on Thursday due to the wildfire smoke.

New York City could see orange skies on Thursday, as dense plumes of hazardous smoke continues pour into the area.

According to the Canadian Wildland Fire Information System, 858 active wildfires are burning on Thursday, including 37 new fires that ignited on Thursday. At least 109 of the wildfires were burning out of control Thursday afternoon, according to the agency.

So far this year, according to the agency, Canada has had 3,549 wildfires that have burned a total of 2.3 million hectares, or more than 93,000 square miles, which is roughly the size of the United Kingdom.

The smoke and ash from the Canadian wildfires was even affecting commercial air traffic. On Thursday, the Federal Aviation Administration (FAA) said it was slowing arriving flights into the Philadelphia International Airport due to low visibility from wildfires smoke.

An American Airlines pilot told Philadelphia air traffic controllers on Thursday that ash was sticking the windshield of his aircraft, according to a recording of the communications provided by ATC.com.

"I've never seen it stick to the windshield like this," the pilot was heard telling air traffic controllers.

American Steve Ventling of Montana told ABC News that he witnessed the Canadian wildfires up close this week