Lee said the bus driver, whose name was not released, was seriously injured and taken to a Phoenix-area hospital. The Arizona Department of Public Safety did not have any details on the driver's condition.

Moments later, the bus with inmates and two Department of Corrections staff members hit the truck as it lay in the westbound lanes of the interstate between Casa Grande and Gila Bend. The crash forced authorities to close the busy interstate for several hours.

Authorities said police received reports around 1 a.m. of a semi-truck that had rolled over on Interstate 8, State Trooper Kameron Lee said.

A prison bus carrying about 50 inmates slammed into a rolled over semi-truck, injuring the bus driver and some 20 inmates, authorities said Wednesday.

The semi had been carrying herbicides, which spilled in the wreck. Officials say the material is not considered hazardous.

The inmates are minimum-security prisoners from Lewis Prison in Buckeye. They were returning from a work detail in Casa Grande.

Around 20 inmates were taken to a hospital for serious and minor injuries. No details were released on their conditions.

Inmates who weren't hurt in the early morning crash tended to the injured and even helped direct traffic, according to the Arizona Department of Public Safety and KPNX.