Seven people are reported to have died in the explosion and collapse of the two buildings in East Harlem in New York's Manhattan on Wednesday following a gas leak tore through the two apartment buildings.
The explosion at 1644 and 1646 Park Avenue, just blocks away from Central Park, blew out windows in cars and buildings in the area, spewed smoke into the air and scattered debris on the surrounding streets, sidewalks and elevated train tracks.
Television images showed heavy smoke and dust rising from the building at East 114th Street and Park Avenue in East Harlem near Columbia University, which reportedly collapsed at about 9 am.
The explosion and collapse of the building disrupted traffic and public transportation has been suspended near the New York City, reports said.
New York Mayor Bill de Blasio said the cause of the explosion appeared to be a gas leak.
''This is a tragedy of the worst kind, because there was no indication in time to save people,'' he said at a news conference.
People living in the area had reported gas odour but the warning came not long before the explosion. The crew dispatched to inspect the area arrived after the explosion, which occurred about 9:30 am.
Two people first reported killed were female, according to the New York City Police Department. A third death was later confirmed by the New York Fire Department. Four additional deaths were confirmed on Thursday.
Dozens of injured people scattered to hospitals across the area. At least 50 people were injured, the Associated Press reported. Two dozen people were taken to nearby Mount Sinai and Mount Sinai St Luke's hospitals. Two people were critically injured, while five had serious but not life-threatening injuries, the fire department said.
The two collapsed buildings had a total of 15 residential units, authorities said.
Hundreds of rescue workers headed to the scene to put out the fire, clear debris, search for victims and transport people who needed medical attention.
''It's going to be a long, extended operation to make sure that we can get through that debris as quickly as possible,'' said Salvatore J Cassano, the fire commissioner.
Gas and power supplier Con Edison said in a statement that it would ''conduct a thorough investigation'' to figure out what caused the explosion. The utility shut down electric and gas service in the vicinity while crews worked to make the area safe, it said.