YOGYAKARTA, Jan. 27 (CNA) - Indonesia’s most active volcano erupted on Wednesday (Jan 27) with a river of lava and searing gas clouds flowing 1,500m 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 5km danger zone around the crater as the local administrations in Central Java and Yogyakarta provinces closely monitor the situation.

The 2,968m 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.

Merapi's last major eruption in 2010 killed 347 people.

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.