(ABC News) -- Two people were killed and at least 64 were injured today when a suspected gas explosion tore through a building in Manhattan's East Harlem neighborhood, collapsing at least part of the structure, authorities said.
“This is a tragedy of the worse kind because there was no indication in time to save people,” New York City Mayor Bill de Blasio said. “There will be a search through the rubble of the building once the fire has been put out.”
"They were right there," one source told ABC News, referring how close the two deceased victims were to the explosion.
At least two women are dead, one in her 30's or 40's, while the other is unidentified, ABC station WABC reported.
At least 64 others were taken to hospital, two with life-threatening injuries, including a 15-year-old boy, authorities said. De Blasio noted that several people were still unaccounted for.
A New York City official said the situation was fluid and the "numbers are going to change."
Plumes of thick smoke engulfed the area like fog around the building at 116th Street and Park Avenue after residents reported hearing a loud explosion around 9:30 a.m. The first 911 call came in at 9:31 a.m. and firefighters were on the scene two minutes later, Fire Commissioner Sal Cassano said.
Con Edison was responding to a report of a gas odor at 1652 Park Ave., officials said. The call came in at 9:13 a.m. from a resident of that building who indicated the odor may have been coming from outside the building. Two Con Edison crews were dispatched at 9:15 a.m., officials said, noting they arrived just after the explosion occurred. The street is served by an 8-inch low-pressure gas main, utility officials said.
Harlem Hospital confirmed it has received 13 patients, including two children with critical injuries, while another 10 adults and a child are in stable condition. Mount Sinai Health released a statement saying it is treating 22 patients, including at least three children, suffering various injuries from smoke inhalation to cuts from broken glass, while St. Luke's Hospital is treating one.
Six of those patients have been released, including two of the children, hospital officials said. New York Presbyterian Weill Cornell currently has 11 patients, including a child under observation and Metropolitan Hospital has confirmed it has received 17 patients, including a child still under observation. Seven of those patients have since been released.
Among the casualties, two FBI agents in the area on unrelated business sustained non-life-threatening injuries in the blast and are expected to make a full recovery, authorities said. An off-duty NYPD officer who lives nearby was also hurt and was taken to the hospital with minor injuries.
The FBI was on the scene, but there is no indication of terror or crime, authorities said.
There are "no indications of foul play,” de Blasio said.
Google images of the building show two commercial storefronts on the ground floor with four floors of residential apartments above those storefronts.
“I was standing in my room when I heard the explosion and the building shook at the same time," said Rosario Valderdo, who lives in the apartment building next door. “The windows were shattered and I grabbed my dog and went outside. The building had collapsed and there were people underneath it and they were trying to take them away from there.”
Neighbors said shattered glass from nearby storefronts and debris littered the ground following the blast.
“The explosion woke me up. The building shook, my mother’s window fell in,” said neighbor Adam Ocasio. “You could see the smoke and debris as soon as you got outside.”
Brandon Whitaker was also sleeping in his home in the nearby Taft Houses when he was awoken with a start.
“My room shook, I was disoriented,” Whitaker said. “Feels like an earthquake right in your room, an earthquake and a car crash right in your room, that’s loud and abrasive. It was shaking, and I thought the Metro-North [train] had crashed.”
There were a total of 15 residential units in the two buildings, six in one and nine in the other. Nine people are currently unaccounted for, but there is no indication whether those people are injured, de Blasio said.
“We are expending every effort to locate each and every loved one," said de Blasio. "We don’t want to speculate who might be in the building and their situation until we have the ability to get closer."
Cassano said it will take a while to get everyone out, but canine search and rescue dogs on the scene have not detected the scent of any other victims at this point, which was a good sign.
Any relatives who are looking for info about their loved ones can call 311 until a special hotline is set up, officials said.
The pastor of the Spanish Christian church located on the ground floor of one of the buildings said some of the congregants had been in the church at the time of the explosion, de Blasio said.
More than 250 firefighters working at the scene to battle the blaze, bringing in dozens of pieces of equipment to clear the rubble.
The Department of Buildings says it has issued full vacate orders to several buildings near the blast site because of firefighting operations, but that they believe the surrounding buildings are structurally sound.
A temporary shelter at a school has been set up at for the Red Cross at PS 57 on 115th and Lexington.
Roughly 100 displaced people and dozens of others inquiring about the whereabouts of family members sought shelter at the school, said Red Cross spokesperson Jamie Dierking.
Residents in the area this morning posted pictures of what remained of the buildings on social media.
All Metro-North train service was temporarily suspended because all Metro-North trains in and out of New York City use the rail lines adjacent to blast zone, said Metropolitan Transportation Authority spokesman Adam Lisberg. All service to and from Grand Central Terminal has since been restored. Services on the New Haven and Harlem line and Hudson Line were also restored this afternoon. Subway service was not affected.
Alex Morrell said he was in his home nearby on 116th and Park Ave. when the explosion shook the neighborhood. He said he was one of the first people on the scene before firefighters arrived.
“You heard this deafening explosion and the building shook. [The weather] was finally nice out so we had the windows open and we saw people started spilling into the street,” Morrell said. “It’s New York City, you hear weird noises all the time, then I started hear someone screaming ‘Dear Jesus! dear Jesus!'"
“An enormous crowd gathered. People were walking toward it and walking away with tears in their eyes. It was extraordinarily emotional,” Morrell said.
ABC News' Dan Childs contributed to this report.