An hour before an apparent gas explosion sent flames soaring and debris flying at a Manhattan apartment building, injuring 19 people, utility company inspectors decided the work being done there was faulty.

The powerful blast on Thursday in the East Village caused the collapse of three buildings and fire damage to a fourth, the fire department said. It left four people in critical condition, more than a dozen others injured and one family searching for a loved one.

Firefighters worked through the night to put out pockets of fire, pouring large volumes of water over the rubble, a fire department spokesman said Friday morning as a steady rain fell.

He said when a building collapses it takes much longer – even days – to put out all the fire.

About 200 firefighters and medical staff remained on the scene.

“Currently we’re in the extinguishing phase, making sure there are no further fires and extinguishing the fires that are there, he said.

The blast caused three five-story buildings to collapse within a few hours of each other, the spokesman said. A fourth, seven-story building, suffered extensive fire damage.

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 for utility company Con Edison had been there, company President Craig Ivey said. But the work failed the inspection, partly because a space for the new meters wasn’t big enough, Con Ed said.

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

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.

Adil Choudhury, who lives a block away, ran outside when he heard “a huge boom.”

“The flames were coming out from the roof,” he said. “The fire was coming out of every window.”

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

De Blasio said it didn’t appear that anyone was missing, but late Thursday Tyler Figueroa, 19, of Manhattan said his 23-year-old brother Nicholas had disappeared after going on a date at an East Village sushi restaurant that was leveled by the explosion.

Figueroa said the couple was paying for their meal when the blast occurred, and that his date, who is in the hospital, remembers only stumbling outside before losing consciousness.

“I just pray my brother shows up,” he said. “We just hope my brother comes back.”

Police said early Friday they have no reports of a missing person.

The explosion and 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 no one had reported a gas leak before Thursday’s blast. Con Edison said it had surveyed the gas mains on the block Wednesday and found no leaks.

Bystander Blake Farber, who lives around the corner, said he’d been walking by the building and smelled gas seconds before the big blast.

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

“We are praying that no other individuals are injured and that there are no fatalities,” de Blasio 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.”

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 debris off a man so he could escape the restaurant where they had been eating.

(AP)