Residents reported hearing a large explosion near Park Avenue and 116th Street in East Harlem at about 9:30 a.m. ET. Two five-story buildings collapsed down to the first floor, littering the area with debris.
Investigators say a gas leak triggered the explosion, which occurred around 15 minutes after a neighboring resident reported smelling gas. The Con Edison utility said it immediately sent workers to check out the report, but they didn't arrive until it was too late. The FBI was on the scene, but authorities say there is no indication of terror or crime.
A tenant said residents had complained repeatedly in recent weeks about "unbearable" gas smells. Investigators are focusing on an eight-inch gas main that fed both buildings and the possibility that an old cast iron pipeline weakened during the harsh winter.
Hunter College identified one of the people killed in the blast as 45-year-old Griselde Camacho, a security officer who worked at the Silberman School of Social Work building. Another of the people who died was identified by family members as Carmen Tanco, 67, a dental hygienist. Police identified a third fatal victim as 21-year-old Rosaura Hernandez-Barrios. The identities of the other two fatal victims were not immediately known.
Sixty-four others were injured. As of 11 p.m., nine occupants of the buildings remained unaccounted for, according to the NYPD. But authorities cautioned that some people may not have been in the building at the time of the blast.
Witnesses said the explosion was so powerful, it knocked groceries off the shelves of nearby stores and shattered store windows for blocks.
"I was standing in my room when I heard the explosion and the building shook at the same time," Rosario Valderdo told ABC News. Valdero lives in the apartment building next door. "The windows were shattered and I grabbed my dog and went outside. The building had collapsed and there were people underneath it and they were trying to take them away from there."
More than 250 firefighters from more than 40 units responded to the scene. Thick smoke blanketed the area, and residents were urged to stay indoors and keep windows closed.
The Associated Press contributed to this report.