All but three of the other 29 people on board suffered injuries.
Civil protection director Alonso Gomez in the Durango state town of Gomez Palacio says the accident happened on Saturday as the bus headed back to his town after a tourist outing.
Gomez yesterday said that the driver reported the brakes failed and he lost control of the vehicle. The driver is injured and in custody while the accident is investigated. The road where the accident happened is narrow and winds through canyons up to 300 metres (nearly 1,000 feet) deep.