A Mississippi school bus driver died when their bus went off a highway Tuesday morning and rolled into a ditch, police said. Seven students were injured in the crash, and two were in critical condition, Mississippi Highway Patrol Captain Johnny Poulos told CBS News.

The bus went off Highway 72 and rolled over several times, Poulos said. No other vehicles were involved in the crash.

Investigators didn't know if the driver had a medical condition or died from injuries suffered in the crash, Poulos said. The bus was transporting students for the Benton County School District.

The county sits along the Mississippi-Tennessee state line and is about 50 miles from Memphis, Tennessee.