The accident took place at the state-level road in Longde county of Guyuan city when the bus with 19 people aboard overturned and fell into a ravine, state-run Xinhua reported.
A total of 53 fire fighters have been sent to the site to carry out the rescue operation, it said.
The bus, registered in Ningxia's neighboring Gansu Province, has a capacity to carry 41 passengers.
