Smoke drifting from ongoing wildfires has prompted New York City officials to issue an air quality alert, advising more than 10 million residents to remain indoors.

The fire, which began Tuesday in Ocean County, New Jersey—near the coastline—has now scorched over 15,000 acres. Located about 54 miles south of New York City, it is only partially contained. Officials say full containment may not be possible until rainfall expected this weekend.

The smoke, which contains harmful particles and toxic chemicals, poses serious health risks. It can trigger asthma, increase the likelihood of heart attacks, and contribute to long-term conditions such as cancer and dementia.

On Thursday, the New York State Department of Health and Department of Environmental Conservation issued a health advisory for fine particulate matter, in effect from midnight to 11:59 p.m. These particles, known as PM2.5, are incredibly small—less than 2.5 micrometers—and can lodge deep into the lungs, causing significant health problems.

The advisory applies to all five boroughs of New York City, as well as Westchester and Rockland counties and Long Island.

In addition to PM2.5, wildfire smoke contains polycyclic aromatic hydrocarbons (PAHs), which are linked to genetic mutations that may lead to cancer.

Due to elevated particle levels, the National Weather Service (NWS) warned that the Air Quality Index (AQI) in the city could exceed 100—a level considered “moderate” but still risky for vulnerable groups such as children, the elderly, and those with respiratory or cardiac conditions.

At these levels, people may experience symptoms like shortness of breath, coughing, and eye or throat irritation.

“When pollution levels are elevated, the New York State Department of Health recommends that individuals consider limiting strenuous outdoor physical activity to reduce the risk of adverse health effects,” the NWS alert reads.

Although no injuries or fatalities have been reported, the Associated Press noted that 12 structures were still at risk as of Wednesday night, after a commercial building and several vehicles were damaged.