The blast, which was caught on camera, collapsed the first floor of the home on Vermont Street in Cypress Hills into the cellar just after midnight.
Six residents were treated for minor injuries. Two were taken to Brookdale University Hospital, while the other four were treated at the scene.
Felicia Ramos lives down the block and was stunned her neighbors weren't killed.
"Boom, I heard the explosion and I came outside and it was a scary," she said. "The whole house shook, and I ran outside and I heard people screaming. And it was like, 'Get out, get out, get out, gotta get out of here.'"
Still, some 54 residents of adjoining buildings were left homeless.
"It was extending to the exposures two and four of the adjoining buildings, and also it was wrapping around," FDNY Deputy Chief Patrick Sherian said. "We had a building on Jamaica Avenue. It was running up the rear of that building, so we had to do searches, evacuate."
Eyewitness News caught up with several residents trying to keep warm on an MTA bus, and Edwin Rodriguez said he smelled gas on Tuesday.
"I complained about the gas leak earlier in the afternoon," he said. "They ignored it, and this was the result. It was a gas leak. I smelled it when I got home from work. I reported it. They ignored it, and this was the result. This is what we get."
The spectacular blast, which was captured on video, will prove crucial to the investigation. The front door to the building was blown clear across the street.
"Everybody kept saying they smelled gas," resident Mychelle Grullon said. "They smelled gas, but nobody went to figure out, like, 'Where's it coming from? Why is it happening? How to stop it.' And then now this happens, and now a bunch of us don't have somewhere to sleep."
Firefighters searched the debris using drones and thermal imaging cameras, making sure all the building's occupants were accounted for.
The Buildings Department will evaluate the structural integrity of the attached homes.
Meantime, the Christmas tree in Rodriguez's apartment was still lit up, but the window in front of it shattered.
He described how he grabbed his 3-year-old daughter and raced out of the building.
"I took everybody out," he said. "My daughters went without no socks, no sneakers, nothing. I just took her, and we just ran out."
He and his family have not been allowed to go back in and were being taken to a hotel.
Investigators say a faulty boiler connected to a gas line appears to have caused the explosion, but the investigation continues.
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