More than 20 Mississippi high school students were taken to hospitals after a bus fell onto its side on a busy highway.

Neither the extent of the injuries nor what caused the bus to turn over Monday was immediately clear. Carroll County Emergency Management Director Ken Strachan tells The Greenwood Commonwealth no other vehicles were involved.

Greenwood school district spokeswoman Margaret Dean says the bus was carrying 40 students and three football coaches back to Greenwood from a camp in Starkville.

Dean says 20 students were taken to hospitals in Greenwood, Winona and Grenada. One was taken by helicopter to a Tupelo hospital.

Strachan says the bus turned onto its side on U.S. 82 between Winona and Carrollton in central Mississippi.

Dean says the bus was being driven by head coach Clinton Gatewood.