The vehicle was traveling in a mountainous area near Puncak, West Java, south of Jakarta Wednesday, CNN reported.
Sutopo Purwo Nugroho, spokesman for the national disaster agency, said the bus, carrying members of different churches in the Indonesian capital, was returning from a retreat in Puncak, a popular holiday destination.
He said the driver might have lost control of the bus after its brakes failed, CNN reported. The vehicle struck a parked truck before plunging into the ravine, he said.
Those injured were taken to hospitals in the area. Other details were not immediately available.