Melanie Eversley and Doug Stanglin

USA TODAY

NEW YORK — Rescuers combing the rubble of two collapsed East Harlem apartment buildings discovered a seventh victim early Thursday as they continued to search for more missing people.

New York Fire Department spokesman Danny Glover said Thursday morning the body was the fourth found overnight. Three bodies were found Wednesday following the massive explosion at Park Avenue and E. 116th Street.

Fire officials said at least 60 people were hurt in the fiery blast that erupted about 15 minutes after a neighboring resident reported smelling natural gas.

Crews used generator-powered floodlights and thermal imaging cameras to identify heat spots -- bodies or pockets of fire -- at the site where two 5-story apartment buildings were reduced to bricks, splinters and twisted metal.

"This is a difficult job, a challenging job," fire department spokesman Jim Long said. He said it was "a very terrible and traumatic scene."

Police said two women believed to be in their 40s were among the dead. Hunter College identified one as Griselde Camacho, a security officer who had worked for the college since 2008.

Earlier, fire officials said nine people were unaccounted for. Mayor Bill de Blasio cautioned that the missing may not have been in the building.

De Blasio said preliminary indications point to leaking gas as a cause.

Some 200 firefighters worked to control the fire that followed the Wednesday morning blast. The buildings, now flattened, also housed a Spanish Christian Church and a piano repair store.

"It felt like an earthquake had rattled my whole building," Waldemar Infante, a porter who was working in a basement nearby, told the Associated Press. "There were glass shards everywhere on the ground, and all the stores had their windows blown out."

The mayor said the explosion occurred at 9:31 a.m. ET, only minutes before a Con Ed utilities team arrived on the scene to check on the reports of a gas leak.

Elhadj Sylla, 54, said he was about a block away at around 8:45 a.m. when he noticed a faint smell of natural gas.

Not long after, he rushed outside after hearing a tremendous explosion, but was unable to see anything through the thick air.

"It was very dark," Sylla said Wednesday. "There was smoke, dust. I thought maybe the train was coming down," he said, referring to the Metro-North commuter railroad elevated tracks across the street on Park Avenue.

"I thought it was the end of the world," he said. "I thought my life was ending."

Desiree Thompson was walking along Park Avenue with a friend across the street when the explosion occurred.

"We heard this loud bang and the glass flew by us," said Thompson, 58. "My eardrums closed. I thought the train had crashed," she said, referring to the Metro-North commuter train.

Normally, Thompson walks on the side of the street from the apartment buildings, but for no particular reason decided to walk on the other side of the street this morning. "If I had been over there, I would be dead," she said.

Stanglin reported from McLean, Va. Contributing: USA TODAY's William M. Welch in Los Angeles; Ken Valenti, The (Westchester, N.Y.) Journal News; Associated Press