The air quality in New York City worsened Tuesday evening and is expected to "deteriorate further" Wednesday afternoon and evening, New York City Mayor Eric Adams said in a statement.

"At this point, the New York State Department of Environmental Conservation has issued an Air Quality Health Advisory for all five boroughs. While conditions are anticipated to temporarily improve later tonight through tomorrow morning, they are expected to deteriorate further tomorrow afternoon and evening," Adams said.

“Currently, we are taking precautions out of an abundance of caution to protect New Yorkers’ health until we are able to get a better sense of future air quality reports," he said.

Adams said students should still go to school on Wednesday, but New York City public schools won't have outdoor activities.

"These recommendations may change based on updated air quality conditions that come in, but, in the meantime, we recommend all New Yorkers to take the precautions they see fit to protect their health," he added.

Smoke from wildfires from Canada was visible on Tuesday night over Yankee Stadium in The Bronx, as the Yankees played the White Sox, video obtained by ABC News shows.

New York City currently has the worst air quality than any other city on Earth, as smoke stemming from wildfires in Canada makes its way across the Northeast, according to the latest data from Swiss technology company IQAir.

The air quality index in NYC is at 196 as of Tuesday evening, followed by Doha, Qatar, and Delhi, India.

The next U.S. city on the list is Detroit, which currently places eighth, according to IQAir. Toronto, Canada, sat in ninth place as of Tuesday night.

The U.S. Environmental Protection Agency has specific guidance for vulnerable groups if the air quality in their area is deemed "unhealthy."

While the agency warns that all people will experience adverse side effects from exposure to the unhealthy air, it said those with heart or lung disease, pregnant people, children and the elderly are most sensitive.

Those groups should consider moving all of their activities indoors until the air quality alert is lifted, the EPA said.

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