Nearby residents were literally shaken up by the explosion and described the scene to Metro.
"It blew me out of my bed," said Jay Virgo, 30, who lives in a building across the street. Her building shook so violently, she said her window fan fell out.
Virgo said she saw four or five people lying on the ground outside looking "lifeless."
"There were people just outside the building, just laying there," she said. "It was so quick. I saw people running. I just started running down the block."
Just outside her building, Virgo found car parts, bumpers and ashes on her doorstep.
Sandra Suro, who lives nearby on 115th Sreet and Madison Avenue, described a horrific scene. "I thought it was a bomb. It sounded like a bomb. I immediately thought of 9/11. We just saw people running, running, running. It was just a scene from 9/11."
Joseph Thomas, who lives on 116th Street and Madison Avenue, said, "It took out the windows and there was stuff flying around in the air. It shook the whole building like a bomb. It was terrible."
Alicia Benjamin said the windows on the other side of her building were blown out. "Ours were intact, thankfully," she said. "We're kind of trying to see if they're going to let us back in anytime soon or if we're gong to have to find someplace to be."
East Harlem resident Andrew Padilla described the scene as "chaotic." Credit: Andrew Padilla
Reinaldo Rosario, 48, who lives on Park Avenue, is waiting to hear about his girlfriend's brother, who lived in the building that collapsed.
"I'm shaking," he said. "[The explosion] was loud. I thought it was our building because the building shook."
Andrew Padilla, 24, is a lifelong East Harlem resident and an independent journalist and filmmaker in the neighborhood. He told Metro, "I heard the explosion. I was a half-mile away and the building began to shake and I smelled smoke. I'm born and raised here so I wanted to figure out what happened."
Padilla said one building looks like it's still smoking and that the scene is filled with police officers. Padilla said gas and electrical problems are common complaints among his neighbors, adding, "It's unfortunate that it takes a huge explosion for people to pay attention."
Even Molley Mills, who lives in West Harlem on 115th Street and Eighth Avenue, said she could hear the explosion from her home.
"It sounded like a dump truck making a huge noise right underneath the window in the street," Mills said. "It was very loud, very metallic, but pretty substantial to the point where I thought, 'Wow, what was that?'"
Mills, 45, said she then looked outside and saw smoke billowing in the air.
"The helicopters turned up and sirens were going everywhere — it was just crazy," she said. Follow Andrea Park on Twitter: @andreapark