Five school children were airlifted to Robertson hospital on Friday morning after an Elwierda Tours bus carrying at least 70 pupils overturned on the old main road between Robertson and Bonnievale.
Captain Patric Lee said the bus, taking the school children to Bonnievale to take part in school sports, skidded off the road and overturned early in the morning.
The bus driver and other children were also slightly injured, he said.
He said the accident was caused by poor visibility and dense mist, but could not tell exactly when it had occurred.
Rescuers were cleaning up the road and representatives of the bus company were expected to arrive at the scene to remove the vehicle.
An investigation into the accident would be conducted, Lee said.
An Elwierda spokesperson declined to comment when contacted on Friday. - Sapa