Japan also issued a tsunami warning for its southernmost islands after the eruption.
Image source, BNPB/EPAIndonesia’s Mount Semeru volcano has erupted, sending ash billowing into the sky and sparking evacuations on the country’s main island, Java.
Authorities raised the volcano’s warning status to the highest level, meaning its activity had escalated.
No injuries have been reported but people were urged to keep at least 8 km (5 miles) from the area.
Japan issued a tsunami warning for its southernmost islands after the eruption.
The increased threat level from three to four also means the danger threatened people’s homes, a spokesman for Indonesia’s Center for Volcanology and Geological Hazard Mitigation (CVGHM) told a national broadcaster.
“Hot avalanches” caused by piles of lava at the tip of the 3,676m (12,060ft) volcano poured from Semeru after the eruption, a spokesman for the National Disaster Mitigation Agency (NDMA) said.
Volcanic ash mixed with monsoon rain is falling on nearby villages and the evacuation of people, including children and seniors, living near the volcano in East Java province had begun, he said.
Mount Semeru began erupting at about 02:46 local time (19:46 GMT), authorities said.
Indonesia sits on the Pacific “Ring of Fire” where tectonic plates collide, causing frequent volcanic activity as well as earthquakes.
Semeru – also known as “The Great Mountain” – is the highest volcano in Java and one of the most active. Its last erupted exactly one year ago, killing at least 50 people and leaving streets filled with mud and ash.
It also follows a series of earthquakes on the west of Java island, located about 640 km (400 miles) east of Indonesia’s capital Jakarta, including one last month that killed more than 300 people.