The two killed were a man and woman, while the injured woman was taken to hospital by paramedics from a private ambulance service in a critical condition, spokesman Robert Mckenzie said.
It appeared the car was the only vehicle involved in the accident.
“The accident happened about 1km north of the Mthunzini toll plaza on the N2 highway in the Uthungulu health district,” he said.
The car came to a rest on the edge of a sugar cane field and because the car was burning, the field started burning.
The fire was extinguished by the local fire department.
The cause of the accident was being investigated by police.