The accident took place at Mengzhai township in Wuyang county, leaving three dead on the spot, a spokesman with the county government said.
Rescuers rushed 22 injured people to hospital.
Ten others died after admission to the hospital, the spokesman said adding that a survivor remains in a coma.
He said the number of passengers on the coach was not immediately known.
The Ministry of Public Security will dispatch a team to investigate the cause of the accident, according to the spokesman.
This is the second major accident in China in as many days.