CNN — At least two people were killed after a massive explosion and raging fire Wednesday morning in Manhattan's East Harlem, authorities said.
Two buildings collapsed in the blast, which may have resulted from a gas leak. Firefighters were still frantically picking through rubble in search of survivors hours later, fire officials said.
At least 18 people were injured. Five of the injured were taken to Harlem Hospital, including a child in critical condition, a hospital spokeswoman said.
A number of people were missing.
The identifies of the two women who died were not available.
Mount Sinai Hospital was treating at least 14 patients, including one with a brain injury, and two children. Three were in serious condition, a spokeswoman said.
More fatalities appeared likely. Fire officials reported that two survivors suffered life-threatening injuries.
Near 116th Street and Park Avenue, once the heart of New York's large Puerto Rican community, about a dozen firefighters tore at mounds of bricks in a search for survivors from the two buildings -- a piano store and an evangelical church.
As gas and electric utility workers tore up pavement in an effort to shut gas lines, people gathered in the streets, many crying.
One woman tried in vain to find her husband, Jordy Salas, who may have been on the second floor of one of the collapsed buildings. She fainted and was taken to a hospital.
"We're expending every effort to locate each and every loved one," Mayor Bill de Blasio told reporters at the scene. "Hopefully we'll find that some of them are in other parts of the city and have just not been located yet."
The cause was unclear, but Con Ed spokesman Bob McGee said the utility received a call about a gas leak at 9:13 a.m. The call came from a resident at one of the newer buildings on Park Avenue. The utility dispatched a truck two minutes later but it arrived after the explosion, the spokesman said.
"This is a tragedy of the worst kind, because there was no indication in time to save people," de Blasio said.
A building department official said one of the two Park Avenue buildings that collapsed received a city permit last year for the installation of 120 feet of gas piping. The work was completed last June. In 2008, owners of the adjacent building, which also collapsed, were fined for failing to maintain vertical cracks in the rear of the building. The condition was not reported as corrected to the buildings department.
There were a total of 15 units in the two buildings, officials said.
The mayor told reporters that the report of the gas leak, which he said came about 15 minutes before the explosion, was "the only indication of danger."
Fire Commissioner Salvatore Cassano said responding firefighters barely missed the blast.
"If we were here five minutes earlier we may have had some fatalities among firefighters," he said. "Not being here may have saved some lives."
Clouds of dark smoke rose over the largely residential area of redbrick tenements and small businesses after the explosion, which some residents said sounded like a bomb.
Hundreds of firefighters responded, many spraying water on the roaring blaze from ladders.
Metro North commuter rail service was suspended as debris from the explosion landed on the elevated tracks across the street, authorities said.
"I heard a big explosion," said a resident who identified herself as Angelica. "I didn't know what was going on. ... My neighbors came banging on my door, telling me to get out. I guess they were evacuating the building. And I couldn't get out. My door was jammed. Everything on my windowsill fell. I guess the impact of the explosion jammed the door as well."
She added, "It was extremely loud. I couldn't even explain it to you, if I could. It was just so loud. It woke me out of my sleep. That's how loud it was."
Molley Mills, who lives nearby, said at the time of the explosion her building rumbled as if the subway was passing beneath it.
"I went outside my terrace and there was smoke pouring out," she said.
The New York police bomb squad responded to the scene, according to a law enforcement source.
Once a predominantly Italian neighborhood, the stretch of East Harlem saw a large influx of Puerto Ricans in the 1950s. It went on to be called Spanish Harlem. In the 1990s, many Mexican immigrants began to move into the area, which has been gentrified in recent years, with many mom-and-pop shops replaced by restaurants and bars.
CNN first learned of this story via Twitter.
CNN's New York bureau contributed to this report.
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