NEW YORK— Rescue workers using dogs and thermal-detection gear searched the rubble Thursday for more victims of a gas explosion that killed at least seven people, while investigators tried to pinpoint the leak and determine whether it had anything to do with New York’s aging gas and water mains, some of which date to the 1800s.
At least five people were unaccounted for after the blast Wednesday morning destroyed two five-story apartment buildings in East Harlem. More than 60 people were injured.
Fire and utility officials said that if the buildings were plagued in recent days or weeks by strong gas odors, as some tenants claimed, they have no evidence anyone reported it before Wednesday.
Robert Sumwalt of the National Transportation Safety Board said the cast-iron gas main, which dates to 1887, under the street had been examined in a crater and was found to be intact.
However, he said that investigators had been unable to conduct a fuller examination because of the rescue effort underway, and that it was still unclear whether the leak came from inside or outside the buildings. He said there had also been a water main break at the site but it was not known if that contributed to the gas explosion or was caused by it. The water main was installed in 1897, according to city records.
Authorities also hoped to reach the basement to examine heating units, meters, and
other equipment that might hold clues to the blast, Fire Commissioner Salvatore Cassano said.
‘‘We can only get conclusive evidence when the fire is out, when the rescue is completed, and we really get a chance to look at all the facts,’’ Mayor Bill de Blasio said.
Aging infrastructure has become a major concern across the country in recent years, especially in older cities in the Northeast, and has been blamed for explosions, floods, and other accidents.
‘‘We know this is a fundamental challenge for New York City and any older city,’’ de Blasio said. But he said the federal government needs to provide more aid to cities.
As cold, stiff winds blew across the still-smoldering debris, construction equipment with iron jaws picked up the rubble, first depositing it on the pavement, then hoisting it onto trucks that hauled it away. Clouds of thick smoke swirled over Park Avenue.
The mayor told firefighters carrying grappling hooks and other equipment: ‘‘I can only imagine, knowing that at any moment you might find a body, how difficult that is.’’
Police identified four of the dead: Griselde Camacho, 45, a Hunter College security officer; Carmen Tanco, 67, a dental hygienist ; Andreas Panagopoulos, a musician; and Rosaura Hernandez, 22, a restaurant cook from Mexico.
Mexican officials said a Mexican woman, Rosaura Barrios Vazquez, 43, was among those killed.
The bodies of two unidentified men were also pulled from the rubble.
At least three of the injured were children. One, a 15-year-old boy, was reported in critical condition Thursday with burns, broken bones, and internal injuries.
A woman was in critical condition with a head injury.
The blast erupted about 15 minutes after someone from a neighboring building reported smelling gas, authorities said. Consolidated Edison said it immediately sent workers to check out the report, but they got there too late.
Con Ed chief executive John McAvoy said the call had been correctly categorized as low priority.
‘‘A single person calling that they smelled gas outside of a building is not something that would warrant a Fire Department response,’’ McAvoy said.