NEW YORK — Using sound devices to probe for voices and telescopic cameras to peer into small spaces, workers searching a pile of rubble from a gas explosion in New York City continued to treat it today as a rescue operation, holding onto the possibility of finding survivors from a blast that brought down two apartment buildings and killed at least eight people.

“We have to think of survivors and work in that way, with hope,” said Fire Department of New York Chief Edward Kilduff.

Police said that at least one person remained unaccounted for after the deafening blast Wednesday morning destroyed two five-story East Harlem apartment buildings at Park Avenue and 116th Street that were served by an 1887 cast-iron gas main.

The search work was slow going, with 40 percent to 50 percent of the debris removed by Thursday evening. Kilduff said a fire was still burning, and the force of the explosion collapsed and pancaked layers of floors. A back wall that still freestanding posed a collapse hazard.

Workers continued to remove debris at the site today, and hoped to make it down to the first floor by Saturday, then move on to the basement.

More than 60 people were injured. Investigators were trying to pinpoint the gas leak and determine whether it had anything to do with the city’s aging gas and water mains, some from the 1800s.