PORTLAND, Maine (AP) — Police are investigating a crash in which a tractor-trailer struck a school bus Tuesday, sending an injured student to a hospital.

The bus was stopped when the tractor-trailer struck it from behind just before 8 a.m. Tuesday in Portland, police said.

One student had injuries that were not life threatening and was transferred to Maine Medical Center, police said. There were 15 students and a driver on the school bus, police said.