A bus driver was killed and 40 passengers injured Saturday morning when the bus crashed into an overturned tractor-trailer blocking Interstate 25 south of Casper, Wyoming.

Wyoming Highway Patrol Sgt. Stephen Townsend said the crash involving the Omaha-based Arrow Stage Lines bus going from Denver to Billings, Montana occurred about 1:40 a.m. He said after the tractor-trailer crashed in the northbound lanes, a second tractor-trailer driver stopped and activated its hazard flashers.

Sgt. Townsend said about three to five minutes later, the driver of the bus apparently didn't see the overturned tractor-trailer and ran into it, pushing it 60-feet down the road. The bus driver was from the Denver area. His name has not been released.

Police said the bus remained upright. Nearly all the passengers were transported to medical facilities. Sgt. Townsend said the driver of the tractor-trailer that crashed was taken to a hospital, but that person's condition is unknown.