Air quality alerts have been issued for states across the Northeast.
Hazy and dangerous fumes from ongoing wildfires in Canada have engulfed the skies over much of the East Coast, prompting serious air quality alerts in over a dozen states.
Canadian officials said firefighters are scrambling to put out the blazes. So far this wildfire season, Canada has seen more than 8.7 million acres burned -- an area larger than the state of Vermont.
Due to low visibility, the Federal Aviation Administration has slowed flight traffic in and out of New Jersey's Newark Liberty International Airport and New York City's LaGuardia Airport.
A ground stop is in effect at LaGuardia, meaning some flights are being held at their origin airport to ease congestion.
The average delay at Newark is about 84 minutes.
-ABC News' Sam Sweeney
The worst air in the U.S. Wednesday morning is in upstate New York from Syracuse to Binghamton, where the air quality has reached the worst level -- "hazardous."
That air will move toward New York City and Philadelphia on Wednesday afternoon and evening.
Tuesday brought the worst air quality to New York City since the 1960s, officials said, with New York City Mayor Eric Adams calling it an "unprecedented event."
The mayor urged New Yorkers to avoid going outside if they can.
Adams warned Wednesday, "Air quality conditions are anticipated to temporarily improve later tonight through tomorrow morning, but they are expected to deteriorate further tomorrow afternoon and evening."
NYC mayor says air quality expected to 'deteriorate further'
-ABC News' Max Golembo
In Toronto, the poor air quality will last into the weekend, officials warned Wednesday.
"Air quality and visibility due to wildfire smoke can fluctuate over short distances and can vary considerably from hour to hour," officials said in a "Special Air Quality Statement." "Wildfire smoke can be harmful to everyone’s health even at low concentrations. Continue to take actions to protect your health and reduce exposure to smoke."
Washington, D.C., public schools have canceled all outdoor activities, including athletic games, for Wednesday due to the poor air quality.
A "Code RED Air Quality Alert" has been issued for the nation's capital.
New York City public schools also canceled outdoor activities.
"We urge everyone to reduce prolonged or heavy exertion outdoors," NYC Public Schools tweeted.
