Unhealthy air in parts of the United States was forecast for another day Friday as smoke from Canada wildfires continued to be brought south by winds, but some improvement has been seen.
New York City had been blanketed by an eerie orange haze that began Tuesday when smoke from wildfires in Canada was carried south.
The city of more than 8 million people had been considered to have the worst air quality in the world this week, but by early Friday it ranked 15th on a list by tracking service IQAir.com.
Air quality alerts covered most of New York state, as well as Connecticut, New Jersey, all of Pennsylvania and Indiana, and parts of Ohio and Michigan, according to the National Weather Service.
More than 400 wildfires were burning in Canada, which is experiencing very warm temperatures and dry conditions, according to Canada's government and U.S. forecasters.
"An area of upper low pressure has and will continue to direct the smoke from the wildfires in Quebec, Ontario and Nova Scotia down into parts of the Midwest, Northeast and Mid-Atlantic through the weekend," the weather service in the U.S. said in a Thursday forecast discussion.
New York City Mayor Eric Adams had warned vulnerable New Yorkers to stay indoors and everyone else to limit their time outside amid the smoke. The weather service said an air quality alert extends into Friday for much of the area.
Other cities, including Philadelphia and Washington, D.C., were also affected. Flights were also delayed or canceled due to conditions.
Philadelphia schools were to operate remotely on Friday out of an abundance of caution, the city's school district said.
New York City public school students who were scheduled to attend classes Friday were also shifted to remote, although a previously scheduled "clerical day" meant that some students would not be attending classes Friday anyway.
The U.S. and other countries have sent or pledged to send firefighters or other help to Canada.
This article was originally published on NBCNews.com