Trooper Rob Hicks said the 5:30 a.m. crash east of Biglerville scattered debris over a quarter-mile area, and the plane was destroyed. He said there did not appear to have been a fire or explosion.
"Somebody had heard a plane that was possibly having some difficulty, but shortly thereafter they heard a crash," Hicks said.
Hicks said autopsies were scheduled for Friday, and authorities planned to use dental records and perhaps DNA to identify the victims. A phone message left for the Adams County coroner was not immediately returned.
The Federal Aviation Administration and National Transportation Safety Board sent investigators to the scene.
The airplane was a Piper PA30 Twin Comanche, but authorities have not disclosed its starting point and intended destination.
Hicks said he did not know if the plane had been landing or taking off, but he was not aware of any nearby airstrips.