The collision between a Fuso bus and a Ford sedan happened at around 7.15am at the intersection of Mallala Road and Navvy Hill Road in Korunye, eight kilometres north of Two Wells.
SA Police said this afternoon that one of the passengers in the car, a 23-year-old woman from Elizabeth North, died at the scene.
The driver of the sedan, a 22-year-old Freeling man, and the other passenger, a 19-year-old Davoren Park woman, were flown to the Royal Adelaide Hospital for treatment. The woman is being treated for serious injuries.
The driver of the bus, a 36-year-old Pooraka man, was taken to the Lyell McEwin Hospital with minor injuries.
Major crash officers are attending the scene and road closures are in place.