NEW YORK - A gas leak triggered an earthshaking explosion that flattened two East Harlem apartment buildings Wednesday, killing at least two people, injuring 36 and leaving more than a dozen others missing. One tenant said residents had complained repeatedly in recent weeks about "unbearable" gas smells.

By evening, rescue workers finally began the search for victims amid the broken bricks, splintered wood and mangled metal after firefighters spent most of the day dousing the flames. Heavy trucks arrived to clear the mountain of debris where the two five-story buildings stood.

The fiery blast on Park Avenue at 116th Street, not far from the edge of Central Park, erupted about 9:30 a.m., around 15 minutes after a neighboring resident reported smelling gas, authorities said. Con Edison said it immediately sent utility workers to check out the report, but they didn't arrive until it was too late.

The explosion shattered windows a block away, hurled debris onto elevated commuter railroad tracks close by, cast a plume of smoke over the skyline, and sent people running into the streets.

"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."

Police said two women believed to be in their 40s were killed. At least three of the injured were children; at least one was reported in critical condition.

Fire officials said more than a dozen people were unaccounted for, but cautioned that some may not have been in the building.

A tenant in one of the destroyed buildings, Ruben Borrero, said residents had complained to the landlord about smelling gas as recently as Tuesday, a day before the disaster.

A few weeks ago, Borrero said, city fire officials were called about the odor, which he said was so bad that a tenant on the top floor broke open the door to the roof for ventilation.

"It was unbearable," said Borrero, who lived in a second-floor apartment with his mother and sister, all of whom were away at the time of the explosion. "You walk in the front door and you want to turn around and walk directly out."

The Fire Department said it was checking its records for any gas complaints at the building.

The block was last checked on Feb. 28 as part of a regular leak survey, and no problems were detected, said Edward Foppiano, a Con Ed senior vice president. He said there was only one gas odor complaint on record from either of the buildings, and it was last May, at the address next door to Borrero's.

In this image taken from video from WABC, firefighters battle a blaze at the site of a possible explosion and building collapse in the East Harlem neighborhood of New York.

It was a small leak in customer piping and was fixed, Foppiano said.

One of the side-by-side buildings had a piano store on the first floor, the other a storefront church.

City records show that the building Borrero lived in was owned by Kaoru Muramatsu, proprietor of the piano business. A number listed for Muramatsu rang unanswered.

Records at the Department of Housing Preservation and Development indicate the agency responded to complaints from a tenant and cited Muramatsu in January for a broken outlet, broken plaster, bars over a fire escape, a missing window guard and missing carbon monoxide and smoke detectors.

City building records don't show any work in progress at either address, but the building owned by the Spanish Christian Church had obtained permits and installed 120 feet of gas pipe last June.

Con Ed said it remains to be seen whether the leak was in a company main or in customer-installed inside plumbing. The gas main that serves the area was made of plastic and cast iron, and the iron dated to 1887, Foppiano said.

"Age is not in and of itself an issue with cast iron," he said, noting that Con Edison has a cast iron replacement program and the pipe was not slated to be removed in the next three-year period.

The National Transportation Safety Board said it was sending a team to investigate. The agency investigates pipeline accidents in addition to transportation disasters.

Just before the explosion, a resident from a building next to the two that were destroyed reported smelling gas inside his apartment and thought the odor might be coming from outside, Con Ed spokesman Bob McGee said. Con Ed dispatched two crews two minutes after the 9:15 a.m. call came in, McGee said. But they didn't get there in time.

The tragedy brought the neighborhood to a standstill as police set up barricades to keep residents away. Thick, acrid smoke made people's eyes water. Some wore surgical masks, while others held their hands or scarves over their faces. Witnesses said the blast was so powerful it knocked groceries off store shelves.

The Metro-North commuter railroad, which serves 280,000 riders a day in New York and Connecticut, suspended all service to and from Grand Central for much of the day while the debris was removed from its tracks, the structural integrity of the elevated structure was checked, and test trains were run past the explosion site to see if vibrations would endanger the rescue effort. Service resumed late in the afternoon.

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." He added: "I only have what I'm wearing. I have to find a place to stay for tonight and organize what's going to be my next steps."

A Red Cross center was set up at a public school, where about 50 people had gathered, including some who were searching for loved ones.

The explosion destroyed everything Borrero's family owned, including the ashes of his father, who died a few years ago. Borrero said he assumes his 5-year-old terrier, Nina, was killed.

But "I have my mother and sister," he said. "I'm happy for that."