A bus plunged from a hill while traveling on Indonesia's main island of Java on Saturday, killing at least 27 people, police said.

Most of the passengers, who were on their way to a hot spring, were from South Tangerang in Java's Banten province.

Police are investigating the cause of the collision but said they suspect the vehicle's brakes failed to work.

All victims have been evacuated from the bus and most have been taken to a local hospital, officers said.

"Our morgue is now at full capacity, we cannot accept more bodies," Subang hospital spokesman Mamat Dudirakhmat told local broadcaster Metro TV.

He said the vehicle's engine apparently lost power while going up a hill and rolled backward and hit a motorbike before falling into a grass field.

Television footage showed police, soldiers and medical personnel evacuating the victims from the upside-down bus, which was carrying more than 40 local tourists. The bus was headed for Tangerang, a satellite city just south of the capital, Jakarta, from West Java's Tangkuban Perahu, a popular mountainous resort.

Road accidents are common in Indonesia due to poor safety standards and infrastructure.