A student was struck by a trailer truck after stepping out of a school bus in Gray on Tuesday.

Dispatchers said part of Route 100 near 135 Lewiston Road was closed as crews responded to the accident around 2:30 p.m.

The Cumberland County Sheriff’s Office says a 13-year-old male student had just exited an SAD 15 Gray/New Gloucester bus and was crossing the road when the accident happened. The boy was semi-conscious and was taken to Maine Medical Center with serious injuries.

Police said the bus had 17 middle and high school-aged children on board. The bus lights and stop arm were activated at the time of the crash.

The driver of the trailer truck was identified as 49-year-old Jeffrey Lane of Farmington.

The cause of the crash is under investigation.