An explosion and the collapse of two buildings Wednesday morning that resulted in at least two deaths in the East Harlem section of New York City are believed to have been caused by a natural gas leak.

In addition to the two confirmed deaths, 22 people reportedly were injured and at least a dozen more have not been accounted for, according to several reports from the scene.

“The explosion was based on a gas leak,” Mayor Bill de Blasio said during a press conference near the collapsed residential buildings at East 116th Street and Park Avenue in Upper Manhattan. The buildings that collapsed, 1644 and 1646 Park Ave., had a total of 15 residential units, officials said. There was also “very heavy impact” on nearby buildings, and “a heavy fire has ensued as well…There was no warning in advance,” de Blasio said.

Based on preliminary information, “the only indication of danger came about 15 minutes earlier, when a gas leak was reported to Con Edison. Con Ed dispatched a team immediately to respond. The explosion occurred before that team could arrive,” the mayor said. In the aftermath, the utility began shutting down gas mains going into an adjacent building, “but that is a detailed and complicated process that requires digging up the ground and a lot of manual labor to turn off all the different supplies of gas to the building.”

Fire Commissioner Sal Cassano said the gas leak was called in to Con Edison at 9:13 a.m. from a building adjoining the two that exploded and collapsed. A call reporting the explosion came into 911 at 9:31 and emergency units began arriving at the scene just two minutes later, Cassano said. At least 250 firefighters and dozens of pieces of emergency equipment were at the scene following the explosion, and Con Edison officials said they had about 75 employees at the site as well.

Con Edison CEO John McAvoy spoke at the same press conference.

“First I want to add that our hearts go out to the loss of life and those who were injured in this, and their families, and our hearts and prayers will be with them,” McAvoy said. “Regarding the reports of gas prior to 9:13, our first indication of any gas leak was at 9:13 this morning, when we received a call of a gas leak at an adjacent building. We dispatched crews two minutes later at 9:15. We do not have any confirmations, although I’ve heard some in the media reports, [but] we do not have any indication at this point of gas leaks prior to 9:13 this morning.”

During a 4:00 p.m. conference call with reporters, Edward Foppiano, Con Ed’s senior vice president of Gas Operations, said some of the pipe in the area were up to 126 years old, but none were considered to have deteriorated enough to have warranted inclusion in the utility’s next three-year pipe replacement program.

“The street outside the building is served by an 8-inch low pressure gas main that is a combination, material-wise, of cast iron and plastic. As we investigate the infrastructure on that block we’ll be able to determine the source of the rupture. We routinely survey streets for gas leaks, and this block was last surveyed on Feb. 28 of this year and there was no problem detected. We’re working with fire officials and outside parties to determine the cause.”

On May 17, 2013, Con Ed was called to 1644 Park Ave. by a customer who smelled gas, and employees repaired a small leak in the customer pipe, Foppiano said. In 2011, Con Ed replaced about 70 feet of gas main in the street in coordination with nearby water service excavation work. “Really that was the only significant history both inside and outside” in the vicinity, Foppiano said.

Gas pipes in the area are a variety of ages and materials, he noted.

“Some of the cast iron piping on that block is dated at 1887, and yet we also have plastic on that block that’s dated in 2011.” Smaller pipes going from the mains into buildings are also a variety of ages, dating from 1987, 2005 and 2011, he said. There is about 150 feet of the cast iron pipe and another 70 feet of plastic pipe on the block where the explosion occurred.

“We have been doing about 50 miles of main replacement a year over the past three years; about half of that is cast iron and the other half is what we called unprotected steel. We have a program that we use to help determine, based on history of the area, age of the pipe, soil conditions, etc, and this pipe was not slated to be replaced in the next three-year period…based on all of the parameters, this pipe was in good shape.”

Nearby buildings were evacuated following the explosion and the city’s Office of Emergency set up a center for affected residents and their families at a nearby school.

The Metropolitan Transportation Authority said it suspended Metro-North railroad traffic in and out of Manhattan due to the incident’s proximity to the tracks. Train passengers traveling to New York City were taken to stations in the Bronx, where they transferred to the New York City Subway for travel to Manhattan.