NEW YORK (CBSNewYork) -- Three people are dead and at least nine people are missing after a massive explosion rocked East Harlem Wednesday morning, leveling two buildings and sending smoke and flames billowing into the air.
At least 70 others were also injured in the blast, which happened at 9:31 a.m. Wednesday on Park Avenue at 116th Street, 1010 WINS reported.
While the FDNY only listed 27 injured patients, many others came to hospitals independently and were not treated by the department.
PHOTOS: Harlem Explosion
The explosion reduced two five-story buildings to rubble. It also shattered store windows for blocks and hurled glass, bricks and other debris throughout the neighborhood.
Witnesses Describe Blast Heard From Blocks Away
As CBS 2's Andrea Grymes reported, cellphone video showed the flames and panic as people rushed to help. One woman was helped away barefoot, while another, whose car was hit, could be seen falling down while trying to get away from the scene.
The explosion and building collapses were so strong they even generated weak seismic signals that were recorded at seismographic stations in New York City, the Lamont-Doherty Earth Observatory said.
Lamont-Doherty Cooperative Seismographic Network is a regional center for the Advanced National Seismic System.
The seismic waves were recorded at both the Central Park station and the Fordham University station in the Bronx at 9:31 a.m.
WATCH: Cell Phone Video Captures Moments After Blast
Witnesses said the explosion could be heard 40 blocks away.
"I came out, looked up and a building was just gone," witness Mack Mayor said. "It's just like a war zone out here."
"Like a bomb, an explosion. Very loud. It scared the daylights out of me," East Harlem resident Wilfredo Cruz told CBS 2's Don Champion.
"I was sleeping in my bed and all of a sudden something blew up and the bed started shaking, the floor. And I said 'what is this,' I thought the world was coming to an end," said East Harlem resident Robert Santiago.
"The smoke started to rise. It looked like something fell because it wasn't like a fire. It just looked like debris smoke, similar to 9/11," said witness Samuel Paul, who was on the 15th floor of a building on 125th Street.
Lashean Daniels, who lives next door to one of the buildings, told CBS 2's Tracee Carrasco the blast ripped the wall out of her apartment and sent her running for her life.
"When we got downstairs we thought it was safe and it wasn't. They started saying 'run, run it's going to explode again' and people were running down the block. It was chaotic," Daniels said.
Witness Jorge Perez says the impact sent another man near the buildings flying through the air.
"As soon as he stepped on sidewalk, that's when it went boom! And I saw him flying," Perez said.
And the haze from the smoke was so thick, rescuers and residents wore masks so they could breathe. Many people had to wear masks.
More than 250 firefighters responded to the scene. By 5 p.m. the flames were finally knocked down.
Victims Included Public Safety Officer, Dental Assistant; 9 Others Still Missing
One of the victims who was killed in the blast was identified as 44-year-old Sgt. Griselde Camacho by Hunter College, CBS 2 reported.
Asthma kept Camacho home from work on Wednesday, CBS 2's Dave Carlin reported.
The college said Sgt. Camacho served as a public safety officer at Hunter since 2008 and worked in Silberman School of Social Work building.
"We are sad to report that, in an explosion that destroyed two buildings in East Harlem this morning, we have lost a member of the Hunter family....Our hearts go out to Griselde's family at this terrible time," Hunter College President Jennifer J. Raab said in a statement.
"We know this is a difficult time for all those who knew and worked with Sergeant Camacho, whether at the Silberman School or as part of the public safety office. All of you will be in our thoughts in the days ahead. We will update the community soon about plans to hold a memorial and about where to send your condolences," the statement said.
A second victim has been identified as Carmen Tanco, 67, who worked as a dental assistant. Both Tanco and Camacho lived at 1644 Park Ave. and were home at the time.
As CBS 2's Dave Carlin reported, Tanco had every Wednesday off from her job, and relatives said that fact doomed her to die in the place she had called home for 40 years.
"It's horrible," said neighbor Maria Barretto. "It's really horrific."
Family members tried calling Tanco's cellphone praying she'd left the apartment before the explosion.
"All my family has been trying to call her all day long, just hoping that, you know, maybe she's in the neighborhood doing something; so running errands or something," said Tanco's niece, Lucina Ortiz.
The FDNY has not yet identified the last victim, who was said to be female, CBS 2 reported.
Meanwhile, the Mayor's office said nine occupants of the building remain unaccounted for, according to Fire Marshals and the NYPD.
Searches of the street have been completed and did not produce any additional victims, the mayor's office said.
"Our hearts go out to all the families involved," de Blasio said at a news conference earlier Wednesday. "We are spending every effort to locate each and every loved one."
Many families were in distress Wednesday night, including the Salas family, with a husband unaccounted for.
"Everybody knows each other from 5, 10, 20, 30 years ago," Barretto said. "Everybody is praying for all these families."
Of the dozens hurt and hospitalized, a 15-year-old boy being treated at Harlem Hospital Center was described as the most critically injured.
The boy suffered broken bones, internal injuries, and was seriously burned.
"He did verbalize some things when he first came in, but he was quite confused and severely injured," said hospital chief of emergency Dr. Reynold Trowers.
A representative of Harlem Hospital Center said the hospital received 13 patients from the explosion. Three patients were children, including the 15-year-old boy in critical condition. The other two were in stable condition. The hospital said 10 adult patients, ranging in age from 20 to 79 years old, were treated and released.
A Metropolitan Hospital Center spokesperson said the hospital had received 19 patients related to building collapse. Six came by ambulance and eleven walked in on their own with minor complaints, the hospital said. All were treated and released.
3 Dead, Several Missing After Explosion Levels Buildings In East Harlem
Doctors said 22 people were at Mount Sinai Hospital, some of whom walked in for treatment, 1010 WINS' Holli Haerr reported. Most of the injuries were minor, but a doctor told Haerr the hospital had one person in critical condition with a head injury, WCBS 880's Rich Lamb reported. Three children were also brought to the hospital. As of late Wednesday night, all but three patients had been released.
NewYork-Presbyterian Hospital said it had 11 patients related to the incident. They were evaluated at Weill Medical College of Cornell University and released.
The two collapsed buildings were 1644 and 1646 Park Ave. The building at 1644 Park Ave. housed the Spanish Christian Church, while the building at 1646 Park Ave. housed the Absolute Piano Store and had 15 apartments above.
Explosion Sends Debris Flying Through Neighborhood
It was unclear if anyone was inside at the time of the blast, but Carmen Vargas-Rosa, who owns the church, said some of her tenants were unaccounted for.
"We fear for at least four of our tenants who may have been in the building at the time," she said. "We can't reach them on their cell."
De Blasio's office said anyone attempting to locate family or loved ones that may have been in the immediate area should contact the Unified Victim Identification System at 311, which is active.
The mayor's office said crews are searching parts of the debris pile, but other areas of the site are not accessible due to a sinkhole that developed in front of the building due to a subsurface water main break, likely caused by the explosion.
The equipment needed to remove additional debris cannot be brought in until the sinkhole has been mitigated, which could take several hours, the mayor's office said.
The Red Cross set up a reception area with food and water at nearby P.S. 57 -- located at 176 E. 115th St. -- for affected residents and their families.
The organization said several teams of disaster responders, including mental health professionals, were on the scene.
"Licensed mental health professionals are providing critical emotional support during this tragedy," the Red Cross said.
Walter Leiva was at the Red Cross reception area. He told Carrasco he hasn't been able to locate his aunt, who lived in one of the two buildings.
"She's not there. She's literally - they telling me my aunt is not there," Leiva said.
Meanwhile, U.S. Rep. Charles Rangel (D-N.Y.), whose district includes the site of the deadly explosions, headed straight to the airport in Washington, D.C. to fly home and be with constituents.
"I could not possibly sleep in Washington knowing of the tragic loss of life and injuries caused by the shocking explosion that occurred in the heart of our District," Rangel said in a statement "As we continue to pray for the families of those killed or injured in today's catastrophic explosion, my staff and I are taking immediate action to help the displaced and those in need."
Rangel said he is working with clergy and other community leaders to assist in relief efforts. They are collecting food and clothing only, while all monetary donations have been directed to the Red Cross.
De Blasio: Gas Leak Caused Explosion
The mayor said the explosion appeared to be caused by a gas leak, saying Con Edison had received a report of a gas odor prior to the explosion.
"This is a tragedy of the worst kind because there was no indication in time to save people," he said.
Con Ed said it had already sent crews to investigate the reported gas leak when the blast occurred, 1010 WINS' Al Jones reported.
"The call came in at 9:13 a.m. from a resident who reported smelling gas inside the apartment, but the resident indicated the odor may have been coming from outside the building," Con Ed spokesman Sydney Alvarez said. "Two Con Edison crews were dispatched at about 9:15 a.m. and arrived just after the explosion occurred."
Con Ed said the explosion happened at 9:31 a.m.
"All electric and gas service has been shut down between East 116th and East 117th streets on the west side of Park Avenue, as well as on the north side of East 116th Street near Park Avenue, as crews work closely with the FDNY to make the area safe and determine the exact cause of this morning's explosion," Con Ed said in a statement released around 4 p.m.
The utility said it has about 75 personnel at the site of the collapse.
Anthony Ferguson, who lives in the neighborhood, said when he heard the explosion, he instantly suspected gas was to blame.
"I told New York City Fire Department five months ago there was a leak in that corner," Ferguson told WCBS 880's Alex Silverman.
3 Dead, Several Missing After Explosion Levels Buildings In East Harlem
Ruben Barrero, who lived in one of the flattened buildings, said his mother called 311 on Tuesday. But Con Ed President John McAvoy denied having any knowledge of the leak before Wednesday morning.
"Our first indication of any gas leak was at 9:13 this morning," McAvoy said.
WATCH: Gas Leak Reported Before Blast
Alvarez said the street is served by an eight-inch low-pressure gas main and that crews were checking gas lines and other structures for any possible leaks.
Vargas-Rosa said she also smelled gas Tuesday night.
"Last night when we came out of church, at the corner outside in the street there was a smell of gas," she said. "I thought it was from the corner store there so I went to the owners and told them and they said they would look into it and then we went home."
Fire Commissioner Sal Cassano said fire marshals were on site and will determine <exactly what sparked the blast.
"Right now, they can't get anywhere near the source of ignition," he said. "Once we get through the debris and the rubble, we will get down into the basement and see where we think it was ignited."
The FDNY said it will remain on the scene throughout the night and well into the next several days to secure the scene and search for those who remain missing.
The NYPD said there is no indication of terrorism at this point. The FBI was on the scene and the National Transportation Safety Board sent a team to help in the investigation as well.
WATCH: Explosion Heard 40 Blocks Away
During an evening news conference National Transportation Safety Board member Robert Sumwalt said the agency will construct a timeline of the event.
"We'll look at the oversight of Con Edison by federal and state officials; regulatory officials, and we'll look at the possibility of any damage, any damage at all, from third party digging."
He said the gas pipeline that exploded was "a distribution pipeline that operates at a relatively low pressure, and it's natural gas, so that's what we're dealing with right now."
Sumwalt said the NTSB will investigate any possible earlier complaints of gas leaks in the building.
"We're looking at all the reports. We're looking at Con Edison call logs to see when the first calls started coming in," he said. "That will definitely be part of our investigation."
Con Ed To Probe Deadly Building Explosion In East Harlem
Con Ed itself will also be looking into the explosion, said spokesman Bob McGee.
Con Ed plans "to bring in a camera to examine the main to determine where there might have been a problem," McGee said.
Several surrounding buildings were evacuated, though none were evacuated due to structural stability concerns, according to the mayor's office.
A full vacate order was issued for for 95 East 116th St., a one-story commercial building, and 1642 Park Ave. due to fire damage and firefighting operations.
Eight apartments of 91 East 116th St. and 18 apartments of 1648 Park Ave. were also evacuated due to proximity to the site and firefighting operations.
Earlier in the day, a drone could be seen flying over the area, Champion reported.
"We've been seeing a drone flying above the building," Champion said. "We assume that it is investigators getting a better vantage point of some of the damage that's been done by this explosion."
Metro-North said the explosion happened adjacent to their tracks. Service in and out of Grand Central Terminal was suspended for most of the morning and afternoon, but was later estored.
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