Emergency services spokesperson William Ntladi said the ambulance was ambushed on Monday after picking up a patient and one of his relatives.
The ambulance driver stopped for someone lying in the street.
A man approached the vehicle, pushed the driver to the passenger seat, took control of the ambulance and pulled off.
"It is not clear if there was a weapon involved or what kind of weapon was used. We are still waiting to gather more information," Ntladi said.
The driver and his assistant in the back of the ambulance were dropped off on the side of the road in Daveyton.
The patient and his relative in the ambulance were dropped off in the neighbouring township of Etwatwa. An ambulance from the Etwata fire station took the patient and his relative to a nearby hospital.
Ntladi said police found the ambulance parked in Qwaggasfontein on Wednesday. Two men inside the vehicle were arrested.