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 could be 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 known for its French fries when he felt the explosion next door. "It just happened out of the blue. ... We were shaking even an hour, hour and a half later."

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.

The state Department of Public Service was monitoring Con Ed's response.

The fire happened a little over a year after a gas explosion in a building in East Harlem killed eight people and injured about 50. A National Transportation Safety Board report released last week said a leak reported just before the deadly blast may have come from a 3-year-old section of plastic pipe rather than a 127-year-old cast-iron segment that came under scrutiny in the immediate aftermath.

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. De Blasio said it didn't appear that anyone was missing.

"We are praying that no other individuals are injured and that there are no fatalities," he said.

The area was evacuated, and the city's health department advised residents to keep their windows closed because of smoke so thick the buildings disappeared from view. At least one family sought help at an American Red Cross relief center set up at a school.

Adil Choudhury, who lives a block away, ran outside when he heard "a huge boom." When he got in sight of the building, "the flames were coming out from the roof. The fire was coming out of every window," he said.

The flames shot as high as 50 feet into the air, witness Paul Schoengold said.

The explosion was so forceful it blew the door off a cafe across an avenue and left piles of rubble on the sidewalk. Finley said his son helped to lift some debris off a man so he could escape the restaurant where they had been eating.

One person was lying on the ground, being attended to by two to three passers-by who were holding his head still, witnesses said. Some described injured people walking on the avenue with bloodied, dazed faces.

One man was climbing up the fire escape, not down, as freelance photographer Michael Seto ran up to the buildings after hearing the explosion in his apartment a block and a half away.

"People were calling to him that the building's on fire - he needs to get down," and he did, Seto said.