Eight people died when an Intercape bus overturned on Alma Road in Welkom early on Monday morning.
The Free State health department said in a Facebook post that the driver of the bus allegedly killed himself after the accident.
"At about 03:30, it is alleged that an Intercape bus, which was travelling from Durban to Upington via Bloemfontein, lost control at a circle in Alma Road just outside Welkom, when it overturned," SAPS spokesperson Brigadier Sam Makhele said in a statement.
Upon arrival at the scene, police discovered the bus lying on its side at the corner of Arrarat and Alma roads.
"Seven other passengers were declared dead and the body of the driver was found hanging on the tree about 300m from the scene itself," Makhele said.
The Free State health department said four woman and three children were among the dead. Another child died later in hospital.
Makhele would not confirm whether the driver had committed suicide.
"We are investigating an inquest in this regard as we cannot come to thay conclusion until we have investigated all circumstances around his death."
Forty-five passengers - with minor to serious injuries - were taken to various hospitals in Welkom.
Free State police have opened are investigating a case of culpable homicide.