State police said troopers arrived to find four bodies inside the store.
Troopers responded to a report of someone shooting people inside Weis Market in Eaton Township, about 25 miles northwest of Scranton, just before early Thursday morning. The store was closed at the time.
A man shot dead three people before killing himself inside a store in northeast Pennsylvania early on Thursday, local media reported. One of those is the shooter.
Their names were not immediately released and police didn't say whether the gunman was an employee or how he otherwise knew the victims.
Authorities called in a bomb squad to investigate the alleged suspect's auto in the parking lot but ruled the scene all clear.