(Adds new death toll)
By Chris Francescani and Edith Honan
NEW YORK, March 13 (Reuters) - Two New York City apartment buildings collapsed on Wednesday in an explosion apparently caused by a gas leak, killing at least six people and injuring more than 40, with several more victims feared trapped in the rubble, officials said.
The blast, which scattered debris across nearby rooftops, brought down the adjoining five-story buildings, with a total of 15 apartments, at about 9:30 a.m. (1330 GMT) on a largely residential Upper Manhattan block at East 116th Street and Park Avenue.
Clouds of thick smoke billowed from the rubble of the apartment houses that had sat above a ground-level church and a piano store in a largely Latino working-class neighborhood.
Pockets of fire and heat smoldered inside the mounds of debris for many hours after the blasts, complicating search-and-rescue operations that continued under flood lights through the night, city Fire Department spokesman Michael Parrella said.
He said city officials estimated that nine people were still missing as of midnight. A police spokesman said five people remained unaccounted for early on Thursday morning.
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 told a news conference the blast occurred 15 minutes after a resident in an adjacent building called Con Edison to complain of a gas odor.
Edward Foppiano, Con Ed's vice president for gas operations, said while the utility could not say for certain what caused the explosion, it was treating the incident as a gas leak. The utility most recently responded to customer complaint about a gas odor in the area in May, but the issue had been resolved, Foppiano said.
The National Transportation Safety Board said it was investigating the "gas explosion and subsequent fire."
Metro-North Railroad, which had shut down train traffic moving through Manhattan while it cleared debris from the tracks, announced in late afternoon it had restored all commuter rail service through the area.
Two women were confirmed early in the day as having been killed, and the body of a third woman was found in the rubble later, police said. Late Wednesday night, search teams pulled the body of a fourth victim from the site, fire department spokesman Khalid Baylor said.
The fourth, fifth, and six victims were two adult males and an adult female, police said.
One of the victims was identified as Griselde Camacho, a campus public safety officer for Hunter College in East Harlem, according to a message posted on the school's website. Her age was not given.
More than 40 people were injured, most of them suffering cuts, broken bones and smoke inhalation, police spokesman Christopher Pisano said.
At least three children were among those hurt. Two were treated for minor injuries and released, while a third was in critical condition, hospital officials told a news conference.
'THE WHOLE BUILDING SHOOK'
"This is a tragedy because there was no time to warn people ahead of time," de Blasio said. "We are expending every effort to locate each and every loved one."
At least three children were among the injured.
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.
"I heard a big explosion. Boom!" said Aisha Watts, who lives in the building next door.
"The walls started crumbling down. The windows were gone," Watts said. The mother of three said she feared she would die but was soon rescued by a neighbor who kicked down the jammed door to her home.
Six blocks away, Robert Pauline's apartment was rocked by the explosion.
"All of a sudden the whole building shook. We had no idea what was going on," said the 56-year-old Columbia University data processor.
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 held at 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.
For a graphic on the explosion, please click on http://link.reuters.com/mys57v (Additional reporting by Anna Hiatt; Writing by Barbara Goldberg; Editing by Alistair Lyon)