Kalahar said the truck driver told investigators he saw the bus and hit the brakes, but couldn't stop in time. Kalahar said the preliminary investigation showed it was foggy at the time and that may have contributed to the crash.
Murry Roark, Bolivar County's deputy coroner, said the student who died was a 10-year-old girl.
Her name is Taliyah McRoy, according to T.L. Redmon Funeral Home in Cleveland.
Kalahar said 13 people were on the bus. At least 10 people were injured in the accident and three were taken by helicopter to area hospitals. It wasn't immediately clear if all the injured were students. Kalahar said the vehicles flipped over and landed on their sides.
Ross Saddler, business manager for Shaw School District, confirmed that it was one of the district's buses. The bus was carrying students ranging from kindergarten through high school.
The Mississippi Department of Transportation said the highways were reopened.
It was the second fatal school bus accident involving a tractor trailer in Mississippi this year.
In February, a truck driver, a bus driver and a teacher were killed when a semi sideswiped one school bus, then collided head-on with a second one on Mississippi Highway 8. One of those buses ended up hanging partially over the edge of an interstate bridge.
At least 17 Ackerman High School students were injured in the Feb. 8 crash. They were coming home from a senior trip to the University of Mississippi at Oxford.
Killed were trucker Gary T. Bailey, 54, of Mantachie; the driver of the second bus, Steven B. Moss, 37; and Ackerman high teacher Phyllis Graham, 53, of Eupora, highway patrol troopers said.