The 2,968-metre volcano is on the densely populated island of Java and near the ancient city of Yogyakarta
Indonesia’s most active volcano has erupted with a river of lava and searing gas clouds flowing 1,500 metres down its slopes.
It was the Mount Merapi’s longest lava flow since authorities raised the volatile volcano's danger level in November, said Hanik Humaida, the head of Yogyakarta’s Volcanology and Geological Hazard Mitigation Center.
The alert level was being maintained for now at the second-highest level, she said, and people should stay out of the existing 5-kilometre danger zone around the crater as the local administrations in Central Java and Yogyakarta provinces closely monitor the situation.
Most active volcano
The 2,968-metre volcano is on the densely populated island of Java and near the ancient city of Yogyakarta. It is the most active of dozens of Indonesian volcanoes and has repeatedly erupted with lava and gas clouds recently.
About a quarter million people live within 10 kilometres of the volcano, according to authorities in surrounding districts.
Merapi spewed ash and hot gas in a column as high as 6 kilometres into the sky in June, but no casualties were reported.
Merapi's last major eruption in 2010 killed 347 people and caused the evacuation of 20,000 villagers.
Indonesia, an archipelago of 270 million people, is prone to earthquakes and volcanic activity because it sits along the Pacific “Ring of Fire,” a horseshoe-shaped series of seismic fault lines around the ocean.
Government seismologists monitor more than 120 active volcanoes.