A man posing as a passenger fired three shots at a bus driver in Redcliffe, KwaZulu-Natal, on Tuesday, killing him instantly.
Provincial police spokesperson Captain Nqobile Gwala said the 31-year-old driver had been driving on Buffelsdraai Road when an unknown man shot him.
The gunman fled in a getaway car.
Gwala said the motive for the shooting had not yet been established.
Reaction Unit South Africa spokesperson Prem Balram said the private security company responded to the scene just after 07:00 where its officers found the man slumped in the driver's seat with three gunshot wounds to his head.
According to witnesses on the bus, a passenger entered the vehicle, drew a handgun and shot the driver in the head, Balram said.
"The suspect had been picked up as a passenger a short distance from the scene.
"Witnesses informed reaction officers that the bus was in motion when the driver was attacked. The vehicle then rolled back for a short distance before coming to a standstill in the centre of the road."
Unconfirmed reports from a witness indicated the man had fled on foot and was picked up by a white VW Polo, Balram said.
Three spent 9mm cartridges were found inside the bus.
Attempts to reach the bus company were unsuccessful.