NEW YORK — Rescue workers using dogs and thermal-detection gear to search rubble for more victims of a gas explosion found an eighth body on Thursday while investigators tried to pinpoint the leak and determine whether it had anything to do with the city’s aging gas and water mains, some from the 1800s.

At least five people were unaccounted for after the deafening blast Wednesday morning destroyed two five-story East Harlem apartment buildings that were served by an 1887 cast-iron gas main. 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.

National Transportation Safety Board team member Robert Sumwalt said the gas main and distribution pipe under the street had been examined in a crater and were found to be intact, with no obvious punctures or ruptures. They had not been torn from the ground, he said.

However, he said NTSB investigators had been unable to conduct a fuller examination because of the rescue effort underway, and it was 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 unknown if that contributed to the gas explosion or was caused by it. The water main was installed in 1897, according to the city.