UPDATE: Police say no one else is missing in the rubble. Latest story here

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Eight people have been found dead in the smoldering rubble of two upper Manhattan buildings leveled by a gas explosion that injured more than 70 others, and rescuers are still sifting through the ruins as they search for three who remain missing.

Rescue crews brought in a backhoe and bulldozer to look for more buried victims as firefighters battled flareups in the wreckage of the two five-story buildings that collapsed Wednesday morning on 116th and Park Avenue, sending tremors as far as a mile and spewing debris for blocks.

Workers were about 40 percent to 50 percent through the rubble by Thursday night, using sound devices and putting telescopic video cameras into small voids to see if anyone was in there.

"We are continuing rescue operations, hoping to find others still alive," Mayor de Blasio said at City Hall Thursday.

FDNY Chief of Department Edward Kilduff told de Blasio as the mayor visited workers in the rubble that most of the victims have been found about 20 feet into the pile, on the left side. Officials said the two buildings were reduced to a pile about three stories high.

The force of the blast was so strong that it registered on the Richter scale at just under .5, according to Columbia University. Smoke billowed into Central Park and could be seen miles away in midtown, and New Yorkers said they felt rumbles as far away as 150th Street. Closer to the collapse, groceries were knocked from store shelves and an ashy film covered streets, sidewalks and cars.



The explosion knocked out windows of surrounding apartment buildings and forced evacuations in seven of them, officials said. The Red Cross said nearly 70 people, half of them children, are displaced and are staying at the Salvation Army.

The only indication of anything wrong before the explosion was a call to Con Edison from a woman in a nearby building, reporting a strong odor of gas just minutes before the blast, the mayor and the utility said. But it was too late.

Seven of the eight victims killed in the explosion have been identified as Griselde Camacho, 44, Carmen Tanco, 67, Rosaura Hernandez, 22, Andreas Panagopoulos, 43, Rosaura Barrios Vazquez, 43, Alexis Salas, 22, and George Amadeo, 44. The eighth victim has not been identified.

Hospitals reported receiving 74 people injured, including one teen and one woman who were both critically hurt. The 15-year-old boy's skin was badly burned, and he had broken bones and internal injuries, doctors said. The woman, who was pulled from the debris, is being treated for critical neck and back injuries.

Most of the people who were injured are expected to survive. At Harlem Hospital, where more than a dozen people were treated, one man who suffered from smoke inhalation described passing out as he ran from falling debris.

"I just kept on going, just trying to get away," he said.

Another man was driving a cab near the Metro-North tracks when he felt the blast.

"He thought the train was falling on top of him, but that wasn't true," his son said. "His car got shattered but he's OK. He's shaken up."

Two on-duty FBI agents who were driving through the area at the time of the explosion were among those hurt, but their injuries were not life-threatening, the FBI said.

A woman who was at her home on 115th Street between Park and Lexington avenues said she heard the explosion and thought it was a bomb. The explosion was near where Metro-North tracks run through Harlem.

"I thought a train had exploded," said Marisa Aquino.

Another woman who said she was watching TV in her home about a block away said the explosion blew out her windows.

"All my windows shattered and I didn't know what it was," she said on NBC 4 New York. She said first responders soon arrived at her building and ordered everyone out.

"It sounded like a bomb. That's what it really sounded like," Trey Dey, a laborer who was working in a nearby basement when the buildings exploded, told NBC 4 New York.

Officials cautioned the firefighting and cleanup process would take time. Jim Long, an FDNY spokesman, said acrid smoke, high winds and cold temperatures complicated efforts Thursday. He called the scene "terrible and traumatic" as firefighters sifted through debris for more potential victims.

The NTSB, which probes pipeline explosions as well as transportation disasters, says the cause of the explosion appears to be a gas leak -- but surprisingly, the pipe in question is still intact.

"That's unlike other pipeline accidents that I've been to where the pipe is thrown out of a crater," said Robert Sumwalt of the NTSB. "This pipe is still in the ground."

Investigators haven't been able to get a close look at the low-pressure service line, which delivers natural gas for cooking and heat to the buildings that exploded. NTSB says it will examine Con Edison's handling of customer complaints, the oversight of Con Edison by federal and state officials, and any evidence of possible third-party damage from digging, among other things.

The Buildings Department said one of the collapsed buildings had six units and the other had nine. One of the buildings had work done in June for 120 feet of gas piping, records show. It has no violations on record.

The other building just to the north had one violation from 2008 related to vertical cracks in the rear of the building. The city said a fine was paid but it was not clear that the condition had been corrected.

Con Edison described the building's gas main as an 8-inch iron and plastic main. In 2011, 70 feet of it was replaced during an excavation project. The utility's CEO said Thursday that the company received only two gas leak calls at the two buildings in three years; the most recent was in May.

Authorities said after initial examinations there was no obvious source of the leak.

The explosion blew debris onto the elevated tracks of the Metro-North tracks above Park Avenue, causing a shutdown of service in both directions for several hours.

The Department of Environmental Protection is monitoring air quality in the area. As high winds kicked up more debris and smoke Thursday, the mayor said the Health Department is recommending residents in the immediate area limit time outside and keep their windows closed.

The Department of Education said 40 students with asthma returned home Thursday morning from a school located about two blocks away. The school was working with families and handling each student on a case-by-case basis.

--Joe Valiquette, Brian Thompson, Brynn Gingras and Kyli Singh contributed to this story