A spokesman for the Guangxi Regional Administration of Work Safety confirmed that Saturday's crash in the city of Hechi killed 11 people on the spot and another two later succumbed to their injuries during treatment, China's Xinhua news agency said.
Meanwhile 50 of the 75 people taken to a local hospital will require additional medical treatment, including four seriously injured individuals.
While local authorities will continue to investigate the accident, initial reports said it occurred when a bus owned by a tourism agency in the Guizhou Province entered the lane of the other bus.
The Guizhou-registered bus was carrying 41 passengers at the time of the accident.
The second bus, traveling in the opposite direction with its 48 passengers, is owned by a tourism company in southwest China's Chongqing Municipality, Xinhua said.