The latest on this story from WABC-TV New York
The fiery blast rocked the neighborhood about 9:30 a.m., shattering windows a block away, hurling debris onto elevated commuter railroad tracks close by, and sending a plume of smoke over the skyline.
People went running into the streets, and the two five-story buildings on Park Avenue at 116th Street, near the northeastern corner of Central Park, were reduced to a burning heap of bricks and metal.
"It felt like an earthquake had rattled my whole building," said Waldemar Infante, a porter who was working in a basement nearby. "There were glass shards everywhere on the ground, and all the stores had their windows blown out."
Con Edison spokesman Bob McGee said a resident from a building next to the two that were destroyed had reported smelling gas inside his apartment and thought the odor could be coming from outside.
The utility dispatched two crews just after 9:15 a.m., but they arrived just after the explosion, McGee said.
Police said two women believed to be in their 40s were killed, and two of those hurt had life-threatening injuries.
Fire officials said more than a dozen people were unaccounted for. Mayor Bill de Blasio said some may have made it to safety.
Four hours after the blast, firefighters were still dousing the flames with water, and rescue workers had yet to venture into the debris to search for victims.
The neighborhood was brought to a standstill as police set up barricades to keep residents away. Thick, acrid smoke rose into the air, causing people's eyes to water. Some wore surgical masks, while others held their hands or scarves over their faces.
Sidewalks were littered with broken glass. Witnesses said the blast was so powerful it knocked groceries off store shelves.
One of the side-by-side buildings had a piano store on the first floor, the other a storefront church. Building Department records don't show any work in progress at either address, but the building with the church had obtained permits to install new gas pipes in June.
A resident of the one of the buildings, Eusebio Perez, heard news of the explosion and hurried back from his job as a piano technician.
"There's nothing left," he said. "Just a bunch of bricks and wood."
Perez, 48, said he shared an apartment with a roommate and was unsure what his next steps would be.
"I only have what I'm wearing," he said. "I have to find a place to stay for tonight and organize what's going to be my next steps."
The Metro-North commuter railroad, which serves 280,000 riders a day in New York and Connecticut, suspended all train service to and from Grand Central while the debris was removed from its tracks.
Associated Press Reporters Verena Dobnik, David B. Caruso, David Crary, Leanne Italie and Meghan Barr contributed to this report.