The truck was subsequently looted by the community and it is alleged that the driver was trampled to death by the looters.
The incident happened on Sunday morning and the driver is from the freight company Time Link Cargo.
Fleetwatch wrote on its Facebook page: “[At) 05:00 [on Sunday], [the truck] was passing through De Doorns when some criminals threw a boulder from a bridge at his truck.
“The boulder hit his windscreen, smashed through it and hit the driver who then lost control of the vehicle.
“There were two drivers in the cab - both South Africans - and while the uninjured driver was trying to free his colleague who was trapped between the steering wheel and the seat, a marauding mob descended on the truck.
“Some went for the goods on the trailer while others climbed into the cab to steal whatever they could lay their hands on.”
Gavin Kelly, CEO of the Road Freight Association, told Netwerk24 that residents of a nearby informal settlement looted the wreck of the truck.
“These incidents happen frequently and it is concerning that this type of lawlessness is allowed. It is shocking what these people do to one another,” he reportedly said.
Western Cape traffic chief Kenny Africa confirmed the incident.