The famous New York City skyline disappeared on Wednesday afternoon as smoke from the Canadian wildfires continued to flow into the region. In the most impacted areas, breathing smoke-filled air is equivalent to smoking 5-10 cigarettes.

Hazy skies, the fiery, red sun, and the smell of smoke caught the attention of residents from Maryland to New England on Tuesday. The air quality spiked to very unhealthy levels across the Northeast on Wednesday morning as wildfire smoke from Canada poured into the region.

According to Accuweather, On Wednesday morning, the famous New York City skyline once again disappeared behind a hazy veil. Photos and videos shared on social media captured the eerie glow of the sun as it rose above some of the most famous skyscrapers in the Big Apple. “Took this on my roof [Tuesday]. Looked apocalyptic,” one Twitter user wrote.

Due to the high concentration of smoke, lights were turned on at Yankee Stadium to illuminate the stadium when the first pitch was thrown between the Yankees and Chicago White Sox.

But it wasn’t just New York City that was enclosed in a blanket of smoke. Cities and towns from Maryland to New Hampshire reported low visibility and hazy skies.

“View of the skyline [Tuesday night]. No filter, pure smoke,” another Twitter user wrote. The smell of smoke was so strong in parts of Pennsylvania that emergency responders received an influx of 911 calls on Tuesday night, ABC6 reported.

While the smoke created jaw-dropping scenes across the Northeast Tuesday morning, it has also prompted a large swath of air quality alerts.

The air quality alerts caution “sensitive groups,” a big category that includes children, older adults, and people with lung diseases, such as asthma and chronic obstructive pulmonary disease.

Kids, who often are encouraged to go out and play, “are more susceptible to smoke for a number of reasons,” said Laura Kate Bender, the lung association’s National Assistant Vice President, healthy air. “Their lungs are still developing, they breathe in more air per unit of body weight.” No one is immune.

It’s a good time to put off that yard work and outdoor exercise. If you go out, consider wearing an N95 mask to reduce your exposure to pollutants.