NYC Building Fire: 4 Critical After Explosion Tears Through NYC Building

— -- Four people were in critical condition and at least 15 others were injured after a building explosion led to a seven-alarm fire in Manhattan's East Village Thursday afternoon.

It was unclear how many people were inside the building when the fire occurred, according to the New York City Fire Department. The incident took place in a bustling area with many restaurants and pedestrians, blocks away from New York University.

"Preliminary evidence suggests a gas-related explosion," said New York City Mayor Bill de Blasio, adding that the investigation is ongoing. He said the incident "appears to have been caused by plumbing and gas work that occurred in 121 2nd Avenue."

Four buildings were affected, including at least two that partially collapsed, said the mayor.

The four people in critical condition include two individuals with burns to their airways and another person who was unconscious following the event, according to FDNY Commissioner Daniel Nigro.

Of the about 250 firefighters who responded to the blaze, four were transported to area hospitals, where one was in fair condition, said the fire department. The conditions of the other firefighters weren't immediately released.

One man, Nicholas Figueroa, was unaccounted for after the fire, his father told ABC News. Nick Figueroa said his son went to lunch in a restaurant at the bottom of the building that caught fire and that a bank statement showed a charge from the eatery.

Figueroa said he has had no contact with his son since the explosion and that investigators began searching for him late Thursday.

Around 3:17 p.m., witnesses reported what sounded like an explosion at Sushi Park restaurant at 121 2nd Avenue, which is at the bottom of a five-story pre-war building that houses a handful of residential units. Had the event taken place during another time of the day, when more residents were in the building, it's likely more people could have been injured or missing.

"Our members arrived in less than three minutes to a scene they certainly didn’t expect -- to see that this explosion blew the front of 121 across the street," Nigro said. "They, for the first 15 minutes, before the building started to collapse, made extremely dangerous searches of these buildings to search for any victims, and were forced out by the subsequent collapse of 123 and 121."

The flames spread next door to 123 2nd Avenue, another five-story building anchored by the restaurant Pommes Frites on the street level. The other buildings that were affected were 119 2nd Avenue and 125 2nd Avenue, said the mayor.

"To the best of our knowledge they were working on the gas in the building. That was the work being done, and right now, the fire marshals and the police department are investigating with all of the people involved," Nigro said about the work that took place in one of the buildings by private contractors. "I’m sure by the end of tonight, we’ll know a lot more."

At 121 2nd Avenue, Con Edison said it was evaluating work by the building's plumber related to a gas service upgrade but the work failed its inspection "for several reasons, including insufficient spacing for the installation of the meter in the basement."

"We had no reports of gas odors in the area prior to the fire and explosion," read the statement from Con Edison. "A survey conducted yesterday (Wednesday) of the gas mains on the block found no leaks. We continue to work with all agencies on the investigation into the cause, and we are praying for the recovery of all the injured."

The Salvation Army set up a reception station at nearby Public School 63 to support residents of the buildings, family members and neighbors. The public can inquire about people who may be missing related to the incident through the phone number 311.

Almost exactly a year ago, another explosion rocked a separate neighborhood in New York City. That incident in East Harlem killed eight residents and injured dozens on the morning of March 12, 2014. The National Transportation Safety Board is still investigating what may have caused the explosion, which destroyed two five-story buildings. The NTSB released a report last week indicating that the Harlem explosion may have come from a new section of plastic pipe installed in 2011.

Witnesses said the street a scene of chaos when the explosion erupted as first responders rushed to the site. There were a series of earlier reports that indicated the firefighters might have been missing after the blast period, but all the first responders were located. At the same time, there was a frantic effort by the fire department to evacuate neighboring structures on a densely crowded block as the fire continued spreading.

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