Five people were discovered dead after a house explosion in western Pennsylvania damaged at least a dozen additional buildings in addition to destroying three of them, according to authorities on Sunday.

Four adults and one teenager were found dead following the explosion on Saturday just before 10.30 am, according to Lanny Conley, the police chief of Plum (about 32km 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 in this region," said Allegheny County Executive Rich Fitzgerald, who is expected to give more data about the deceased.

According to Steve Imbarlina, the deputy director of fire and emergency services for Allegheny, among the three admitted to hospitals, two were soon after released, while the third was still in serious condition. At the site, 47 firefighters received minimal medical care.

"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.

After the explosion destroyed one house and left two others in flames, emergency personnel discovered people trapped under debris, according to County's Communications Director, Amie Downs. Water tankers from Allegheny and Westmoreland counties assisted the firefighting efforts of at least 18 fire departments.

Together with borough and county law enforcement, the county fire marshal's office is looking into what caused the explosion. Imbarlina cautioned that the probe would be a "slow and long process" that may take "months, if not years" to complete and include a great deal of forensic testing.

Locals who live close to the explosion's site described a "chaotic aftermath".

Rafal Kolankowski, who also lives close to the explosion site, the blast damaged the windows in his home and knocked him and his wife to the ground.

He claimed that after checking on his son, he stepped outdoors and discovered a woman who was covered in white ash.

"It looks like a war zone," he added. "It looks like a bomb hit our neighborhood, and it's just unfortunate."

Officials stated on Sunday that a plan was in place to start restoring service, with electric power expected to be restored to all but a few households. Gas and electric service had been switched off as a precaution.

Governor Josh Shapiro said he and his wife were praying for those affected and promised them that "as you rebuild, we will have your back."