PLUM, Pa. — Five people were found dead after a house explosion in western Pennsylvania that destroyed three structures and damaged at least a dozen others, authorities said Sunday.

Plum Borough Police Chief Lanny Conley said the bodies of four adults and one adolescent were recovered after the blast shortly before 10:30 a.m. Saturday in the borough, about 20 miles east of Pittsburgh.

“This is certainly a sad, sad day and a sad time, for not just the folks in Plum but all the folks in the community and this region,” said Allegheny County Executive Rich Fitzgerald.

Of the three people taken to hospitals, two were released while one remained in critical condition, said Steve Imbarlina, deputy director of fire and emergency services for Allegheny County. Fifty-seven firefighters were treated at the scene for minor issues.

The Allegheny County Medical Examiner’s Office is expected to provide additional information about the deceased victims.

“Please give us some time to deal with this situation and give the families your respect and give them some space to deal with this tragedy,” Conley said.

Emergency responders reported people trapped under debris after the blast leveled one house and left two others engulfed in flames, county spokesperson Amie Downs said. Crews from at least 18 fire departments worked to douse the flames with the help of water tankers from Allegheny and Westmoreland counties.

The cause of the explosion is under investigation by the county fire marshal’s office along with borough and county law enforcement. Imbarlina warned that the investigation would be a “slow and long process” that would include a lot of forensic testing and could last “months if not years.”

Michael Huwar, president of Peoples Gas, said the company’s checks for gas leaks underground and in the air as well as the consistent pressure verified at regulation stations indicates that “our system was operating as designed.”

Gas and electric service was shut off as a precaution, and officials said Sunday a plan was in place to begin restoring service with electric power expected to be returned to all but a few residences, officials said.

Gov. Josh Shapiro said he and the first lady were “praying for the families” affected and promised them that “as you rebuild, we will have your back.”