Federal investigators have begun their preliminary investigation into Wednesday's deadly explosion and building collapse in East Harlem and say it remains a "active search and recovery" operation.
Eight people are confirmed dead and at least 40 others were injured.
The blast, which occurred around 9:30 a.m. Wednesday, led to the collapse of 1644 and 1646 Park Avenue.
The buildings also housed the Spanish Christian Church and piano repair shop on the ground level.
Officials say 44-year-old Griselde Camacho, a public safety officer at Hunter College, 67-year-old Carmen Tanco, a dental hygienist, 44-year-old Andreas Panagopoulos, a musician, 22-year-old Alexis "Jordy" Salas, a junior at the John Jay College of Criminal Justice, 44-year-old George Amadeo, 44-year-old Rosaura Barrios and 22-year-old Rosaura Hernandez-Barrios were killed in the blast.
Panagopoulos and Amadeo lived at 1646 Park Avenue, according to police.
Police say that Camacho, Tanco, Salas and Hernandez-Barrios lived at 1644 Park Avenue.
The city is working to identify the other victim, who they say is a female.
Panagopoulos' family plans to take his body back to his home country of Greece to be buried.
Rescue crews at the scene dealt with heavy winds and bitter cold temperatures Thursday as they scoured through a massive pile of debris where the two five-story residential buildings once stood.
Speaking to reporters Thursday, National Transportation Authority Board Member Robert Sumwalt described the scene as "devastating."
"You've got basically two five-story buildings that have been reduced to essentially a three-story pile of bricks and twisted metal," Sumwalt said.
Sumwalt said that investigators are working under the assumption that the explosion was caused by a gas leak, but they can't get close enough to inspect the pipes until the New York City Fire Department says that the scene is safe.
"The pipe is still intact. That's unlike other pipeline accidents that I've been to where the pipe is thrown out of the crater," he said. "This pipe is still in the ground."
The NTSB is at the scene because it also oversees accidents involving the transportation of gas.
The agency is requesting all Con Edison information and records related to the event and for any others in the past involving gas. It also wants 311 and 911 calls, as well as interviews with victims and first responders.
Along with the explosion, there was a water main break at the site, and it's unclear if the explosion caused the water pipe to burst or if the water caused the gas explosion.
"It's too early to decide that, but we will look at that also," said Fire Commissioner Salvatore Cassano. "We're going to try working with Con Ed and we'll get back out into the street. But mainly, we got to get rid of the debris first. We got to make sure that there is nobody else in the area. We got to do that first."
In the last three years, Con Ed said that it only received two reports of gas leaks at the buildings involved in the collapse.
John McAvoy, the company's CEO, said that one was in January of 2011 and the other was in May of 2013.
He said that both leaks were on internal customer equipment and that both were repaired quickly.
McAvoy said that there was no indication that anything was wrong with the main gas pipeline that runs underneath the whole block.
"We survey them every year for gas leaks, and it's with a mobile device that's extremely sensitive to any leak. We last surveyed this pipe in July on 2013, and no leaks identified at that time," he said.
"We went back 30 days, and there was not a report of a gas leak in any of the two buildings, 1644 or 1646, or any of the other surrounding buildings," Cassano said.
Con Ed received a call about a smell of gas about 15 minutes before the explosion, and a crew was on the way when the buildings collapsed.
McAvoy said that the man who reported the smell told Con Ed that he had also smelled gas the night before but did not make a call at that time.
Speaking to reporters Thursday, Mayor Bill de Blasio said that 89 residential units have been evacuated in the area, leaving dozens of people temporarily homeless.
They are being sheltered by the Red Cross and Salvation Army.
De Blasio said that recovery services will be available to all residents affected regardless of immigration status.
Earlier on Thursday, de Blasio visited first responders working at the site of the gas explosion.
During his tour of the destruction, the mayor offered words of encouragement and admiration to the crews working there, acknowledging what they are doing at the site is not easy.
The work is a coordinated effort between police, fire, Metro-North and other agencies.
A sinkhole that developed near the blast site has hampered the ability to bring in large equipment for the search efforts.
The mayor also addressed the air quality in the neighborhood, saying it is constantly being monitored.
East Harlem residents are being asked to limit their time outside because of the dust and smoke still in the air.
Doctors at area hospitals said that they're seeing a stream of patients suffering from respiratory illnesses.
"Symptoms from asthma can come days after being exposed, and so people should be on the look out for those and think about, even though the fires have been put out and the exposure might have ended, the asthma attack might have already started percolating," said Perry Sheffield of the Pediatric Environmental Health Specialty Unit.
The area already has notoriously high rates of child asthma, and many students at nearby P.S. 57 went home early Thursday because of the smoke.
"Classes are going everywhere 'cause of the smell, and then, I was in another class 'cause of my asthma, so my mom had to come pick me up," said one student.
"It's been causing me a little bit of problems, and my chest has started to hurt," said another. "It smells like gas or maybe something that's burned."
The Department of Education said that the air quality of the school itself was tested and was deemed safe.