(Reuters) - A supermarket employee fatally shot three co-workers before killing himself inside the store in northeast Pennsylvania early on Thursday, state police said.

Randy Stair opened fire at a Weis Markets in Eaton Township, about 25 miles (40 km) northwest of Scranton, shortly before 1 a.m. EDT (0500 GMT), Pennsylvania state police said. The 24-year-old was carrying two pistol-grip shotguns in a duffle bag when he arrived for his overnight shift at 11 p.m. on Wednesday, police said.

Stair killed Terry Sterling, 63, Victoria Brong, 26 and Brian Hayes, 47. He continued firing throughout the store before fatally shooting himself in the head, police said.

It was not immediately clear to police why Stair shot the three employees.

State troopers responded to the scene shortly after receiving a 911 call from a witness who escaped the store unharmed, according to a statement from the Pennsylvania state police.

The store had already closed at the time of the shooting, police said.