Firefighters try to extinguish a fire at the site of a building collapse in Harlem, New York, March 12, 2014. [Photo/Agencies]

Two New York buildings collapsed on Wednesday in an explosion believed to be caused by a gas leak, killing two people, injuring at least 22, and setting off a search for more feared trapped in the debris, officials said.

A blast that scattered debris onto nearby rooftops brought down neighboring five-story buildings with a total of 15 apartments at about 9:30 am (1330 GMT) on the largely residential block at East 116th Street and Park Avenue in Upper Manhattan.

Clouds of thick smoke billowed from the rubble of the apartment buildings that sat above a ground-level church and a piano store in a largely Latino working-class neighborhood. Officials declined to give a number of people still missing.

Mayor Bill de Blasio, who rushed to the scene in East Harlem, where a cascade of twisted and burnt metal blocked the sidewalk and covered parked cars, said preliminary information showed the explosion was caused by a gas leak.

Officials at the press conference said the blast occurred 15 minutes after a resident in an adjacent building called Con Edison to complain of a gas odor.

Hundreds of firefighters were scouring the mounds of debris for survivors and trapped bodies.

"There are a number of missing individuals," de Blasio said. "We are expending every effort to locate each and every loved one."

Crews also scrambled to clean up the debris, which littered nearby train tracks and shut down Metro-North Railroad service, ahead of the evening commute.

Neighbors said they thought an earthquake was shaking them from their beds and breakfast tables. The explosion, which could be heard from blocks away, shattered windows around the neighborhood.

"All of a sudden the whole building shook. We had no idea what was going on," said Robert Pauline, 56, a Columbia University data processor whose apartment six blocks away was rocked by the explosion.

The force of the blast blew Joseph Concepcion, 30, who lives less than a block away, at least an inch off his couch.

"I literally got lifted off my couch, the boom was so strong," Concepcion said.

President Barack Obama was briefed on the collapse and sent his condolences to the victims' families and his support to first responders at the scene.

"Our thoughts and prayers go out to everyone impacted by this incident," the White House said in a statement.

Crowds of residents, their faces covered with protective scarves and masks, filled the sidewalks of surrounding streets, which were blocked off with yellow police tape.

"It's a very active scene. It's a very chaotic scene," said Fire Department spokesman Michael Parrella.

Fire trucks used high cranes to spray blasts of water into the rubble, as dozens of ambulances and police cruisers with flashing lights swarmed the scene.

During the morning commute, trains were stopped in nearby stations because of debris on the tracks and passengers were ordered off the Metro-North Railroad cars at the Fordham stop in the Bronx, passengers said.

Metro-North said it had been rerouting commuters to New York City subways and it was not yet clear whether normal train service would resume in time for the evening rush hour.