NEW YORK (AP) — An explosion at a New York City apartment building blew off a massive chimney that ran up the side of the high-rise, leaving residents to wait for clearance to return to their apartments as officials investigate what caused the blast.

A plume of dust covered the block in the aftermath of the explosion, which left a huge pile or bricks around the building's base and on a nearby playground. The building stood with a 20-story gash in its side.

As residents and officials wait for more answers, here is what to know about the collapse.

No injuries or deaths were reported in the collapse of the chimney, which vents exhaust from the boiler room that provides heat to the Bronx building.

Residents reported hearing a blast just after 8 a.m. Investigators were trying to determine if there was a gas leak or whether something else triggered the explosion, Mayor Eric Adams said.

Apartments in the building weren't seriously damaged, though some had their air conditioners ripped from windows by the falling bricks. Firefighters sifted through the rubble and sent rescue dogs bounding over the pile to look for any victims, but found none.

“We avoided a major disaster here,” Bronx Borough President Vanessa Gibson said at a news conference.

Still, some apartments were evacuated as a precaution while inspectors assessed the damage.

The building was part of New York City's huge and aging public housing system. Buildings in the system average roughly 60 years old, according to the New York Housing Authority. The complex of buildings where the collapse occurred was built in 1966.

A 2023 Physical Needs Assessment conducted by the city’s housing authority estimated that the Mitchel Housing complex would need nearly $726 million in repairs over the next 20-years. The highest infrastructure need was listed as “Heating.”

Around half a million New Yorkers live in the aging buildings run by housing authority, which is the country's largest public housing system. Tenants have complained for decades about dangerous or unsanitary conditions, including rodents, mold, and heat and hot water outages.

In 2019, a federal monitor was appointed to address chronic problems like lead paint, mold and lack of heat. When he wrapped his five-year term in 2024, the monitor, Bart Schwartz, noted that the overarching issue for residents remained the “poor physical state of NYCHA’s buildings.”

City officials are investigating what went wrong.

The city’s Emergency Management Commissioner, Zach Iscol, said building inspectors are checking the building’s foundations and the apartments to make sure they are sound.

“Right now we're kicking into the next phase of this, which is recovery,” Iscol said, adding that the city was working to restore heat and hot water services to the building. The mayor said the building will be repaired.

Iscol said that the city opened up a reception center for impacted residents to receive resources like food and other necessities.