MONTGOMERY, Ala. (AP) -- Police are investigating a four-vehicle crash south of Montgomery that left two people hospitalized.

Authorities say the crash occurred around 3:50 p.m. in the northbound lanes of U.S. 231.

Police say a Montgomery County school bus carrying five people, a pick-up truck, an 18-wheel car hauler and a box truck collided.

The cause of the collision was unclear Wednesday night.

Police say the driver of the pick-up was entrapped and was later hospitalized with non-life threatening injuries.

The driver of the box truck was also hospitalized.

Authorities say the occupants of the school bus and the 18-wheeler were not injured.

State troopers are investigating the accident.

AP-WF-01-17-13 0053GMT