The Sileri Crater at Dieng Plateau erupted spewing cold lava, mud and ash 50 meters into the sky, said National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho.
The sudden eruption occurred while about 17 visitors were around the crater. Ten people were injured and were treated at a hospital.
Soldiers and police officers were dispatched and local residents and visitors were asked to evacuate in case of further eruptions, Nugroho said. The crater appeared to be quieter Monday morning, and all visitors to the plateau have been evacuated.
Sileri is the most active and dangerous among some 10 craters at Dieng Plateau. Its most recent eruption was in 2009, when it unleashed volcanic materials up to 200 meters (656 feet) high and triggered the creation of three new craters.
Dieng Plateau, located in the Central Java district of Banjarnegara, is a popular tourist attraction because of its cool climate and ninth-century Hindu temples. It sits about 2,000 meters (6,600 feet) above sea level.
Soldiers and police officers were dispatched to the scene, while local residents and visitors were asked to evacuate the area in case of further eruptions.
Of those sent to the volcano, at least two people were killed and several more remain missing after an Indonesian search and rescue helicopter crashed.
The helicopter was carrying at least eight people including four crew when it hit a cliff in Temanggung, Central Java province, late Sunday afternoon, a senior official at the social affairs ministry said.
