NEW YORK - An apparent gas explosion leveled an apartment building, largely destroyed another, and launched rubble and shards of glass across streets in the heart of Manhattan's trendy East Village on Thursday, injuring at least 19 people. Smoke was seen and smelled for miles.

Restaurant diners ran out of their shoes and bystanders helped one another to escape the midafternoon blast, which damaged four buildings as flames shot into the air, witnesses said. Passers-by were hit by debris and flying glass, and bloodied victims were aided as they sat on sidewalks and lay on the ground, they said.

"It was terrifying - absolutely terrifying," said Bruce Finley, a visitor from San Antonio, Texas, who had just taken a photo of his food at a restaurant when he felt the explosion next door.

Mayor Bill de Blasio said preliminary evidence suggested a gas explosion amid plumbing and gas work inside the building that collapsed was to blame.

A plumber was doing work connected to a gas service upgrade, and inspectors from utility Con Edison had been there to check on a planned meter installation about an hour before the fire, company president Craig Ivey said. But the work failed the inspection, partly because a space for the new meters wasn't big enough, and the inspectors said gas couldn't be introduced to that part of the building, Con Ed said.

De Blasio noted that no one had reported a gas leak to authorities before Thursday's blast. Con Edison said it had surveyed all the gas mains on the block Wednesday and found no leaks.

Firefighters continued pouring water on the buildings for hours after the blast, in an area of old tenement buildings that are home to students and longtime residents in an area near New York University and Washington Square Park.

Firefighters said at least 19 people were hurt, four critically, some with burns to their airways.

The area was evacuated, and the health department advised residents to keep their windows closed because of smoke so thick the buildings disappeared from view.