The accident took place in Kaiyang, an outer county of the provincial capital Guiyang, the county government said in a statement.
The 19-seater bus, en route from Kaiyang to Weng'an county in Bouyei-Miao Autonomous Prefecture of Qiannan, veered off a bridge and fell into the river, state-run Xinhua news agency reported.
At least 13 people were killed and six others injured in the accident, the report said, adding that a probe has been launched into the accident.
Fatal road accidents are a serious problem in China, where traffic regulations are often flouted.
The country's frequently overcrowded long-distance buses are prone to accidents, with individual incidents regularly causing dozens of deaths.
Disclaimer: No Business Standard Journalist was involved in creation of this content