The vehicle was travelling on a bridge on Tuesday in Anshun, Guizhou province when it crashed through a roadside barrier and fell into the water.
Those on board reportedly included students who were scheduled to take the "gaokao" university entrance exams, state media said.
The cause of the crash is currently under investigation.
The driver, who is among the dead, had wokred on this bus route since 1997, Xinhua said.
It's unclear how many people were on the bus at the time and how many of those were students.