By Matt Smith
It shook upper Manhattan for blocks, and when it was over, a five-story apartment building and its neighbor were gone.
After Wednesday morning's deadly building explosion in East Harlem, squads of firefighters dug through piles of shattered bricks and beams. Ladder trucks sprayed water into the gap where the buildings once stood. As Detective Martin Speechly, a New York police spokesman, put it: "1644 Park Avenue appears not to be there anymore."
Along with that structure -- a five-story apartment building -- a neighboring piano store and a Latino evangelical church collapsed as the blast rippled throughout the neighborhood. Angelica Avila told CNN she was trapped in her apartment down the block for a short time afterward.
"My neighbors came banging on my door. I guess they were evacuating the building, and I couldn't get out -- my door was jammed," she said. "Everything off my windowsill fell, and I guess the impact of the explosion jammed the door as well."
Her stepmother had to sneak in through the back to try and open the door for her, she said.
Three blocks away, the blast knocked Klay Williams off his feet as he brushed his teeth before work. He told CNN's sister network HLN that his first thoughts were a possible terrorist attack, "as New Yorkers, we tend to do," or maybe a derailment of the nearby Metro-North commuter line.
"I went to my back window, because I'm on the very top floor," he said. Looking down the street, he saw "a bunch of people just running, as if they were running towards something."
Authorities suspect the explosion was the result of a gas leak reported a short time before.
Seven blocks away, Eric Boise could feel his apartment shake and saw others "pouring out of the apartment buildings at 116th and Madison Avenue." He followed himself, watching as firefighters hauled gurneys into the wall of smoke to bring out the wounded.
"I can see in front of me about 50 feet up until the explosion, and then it gets pretty thick," Boise told CNN.
Michael Mowatt-Wynn, the head of the Harlem & the Heights Historical Society, called the surrounding area "a community in transition." Its population of 100,000-plus was once largely Italian. In the late 1950s, large numbers of Puerto Ricans moved in -- in part because of the similarities between their native Spanish and the Italian still spoken there.
The 1990s brought a growing Mexican population, and now the area is being gentrified, Mowatt-Wynn said. It's home to a lot of mom-and-pop businesses and restaurants, and New York University is building a new dormitory in the area, he said.
The full toll was uncertain early Wednesday afternoon, but at least two people had been reported killed. The gas leak had been reported only 15 minutes before the explosion, Mayor Bill de Blasio told reporters.
"This is a tragedy of the worst kind, because there was no indication in time to save people," he said.
CNN's Poppy Harlow, Rose Arce, Chris Kokenes and Ray Sanchez contributed to this report.
™ & © 2014 Cable News Network, Inc., a Time Warner Company. All rights reserved.