Authorities responded to the crash in Mississippi's Warren County at around 12:40 a.m., the Mississippi Highway Patrol said in a news release. The bus was traveling westbound on Interstate 20 when it veered off the highway and overturned. Authorities did not say what caused the bus to leave the roadway, CBS News reported.

Six people were pronounced dead at the scene, the MHP said, and one person died at Merit Health Hospital in Vicksburg. 

Thirty-seven other passengers were taken to local hospitals in Vicksburg and Jackson with "unknown injuries," the MHP said. A person identified as the co-driver of the bus was not transported.  

None of the victims have been publicly identified. No other vehicles were involved in the accident. 

The crash is being investigated by the Mississippi Highway Patrol and the Commercial Transportation Enforcement Division.