The official Xinhua News Agency says the accident occurred early Wednesday and the cause was not immediately clear.
It says 45 people were on the bus, which was headed from eastern Jiangsu province to the coastal city of Xiamen in Fujian province. It overturned in Fujian's Ningde city.
Road safety is a serious problem in China, with many accidents caused by poorly maintained roads and bad driving habits.
Fifteen people were killed when a bus crashed into a ravine in northern Shanxi province in February.