The most effective way to protect yourself during wildfire emergencies is to stay indoors or limit time outdoors when there is smoke in the air, according to the Centers for Disease Control and Prevention. This is especially important for those with heart or lung conditions who are at higher risk for adverse health effects.

If you can, try to avoid exercising outdoors until the air quality improves, especially those with underlying lung disease.

"People with asthma and people who already have lung disease or underlying lung problems, it can exacerbate that, it can irritate that. And if the air quality is bad enough, it can even cause some symptoms of feeling unwell and respiratory symptoms in people who are healthy," said Dr. Stephanie Widmer, a member of ABC News' Medical Unit.

Pregnant people should also try to avoid spending time outdoors, especially those who are further along, Widmer said.

You should wear a mask that covers your nose and mouth, fits tightly to your face and can filter out smoke or ash particles before you breathe them in, according to the CDC. N95 or P100 masks can help protect your lungs from smoke or ash.

Click here for more tips on how to stay safe.

-ABC News' Nadine El-Bawab and Youri Benadjaoud

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."

-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."