Witnesses said the bus suddenly went careening down Co Ma Pass, almost blocking the road.
It was carrying 30 foreign and 10 Vietnamese passengers.
Thirteen injured passengers were taken to the Khanh Hoa provincial general hospital for treatment.
Among them were seven foreigners who had broken arms or suffered injuries in their bodies, said Nguyen Van Xang, director of the hospital.
The foreigners were identified as Liam Donneliy, 20, Jonas Lion, 22, Anmelies Claeskens, 21, Melissa Poulton, 18, from the UK, Casse Rtom Melsen, 21, from Denmark, Boghait Lucie, 27, and Bovin Sinon, 28, both from France.
Xang said all the patients were in stable condition.
VOV