A box-trailer fire Saturday closed traffic on Interstate 79 near the Portersville exit for about an hour and backed up traffic for hours afterward, state police said.

The fire was reported at 4:08 p.m. Saturday to Butler County emergency services. Harmony Fire District and Portersville and Prospect fire departments were dispatched. Harmony ambulance was also on the scene.

The cause of the trailer fire is not yet known; however the contents had to be cleaned up and removed, officials said.

The interstate section effected was from Exit 99, Route 422 in Butler/New Castle, to Exit 96, Portersville/Prospect.