The Mount Merapi volcano on Indonesia’s Java island has spewed searing ash and other volcanic debris that poured down its slopes on Wednesday, the country’s geological agency said.

Pyroclastic flows – a fast-moving mixture of extremely hot rock fragments, gas, and ash – blasted from the volcano for four hours in the early morning, according to the Research and Development Center for Geological Disaster Technology, which monitors the volcano.

There were no reports of casualties and the alert level remained at the second-highest level, it said.

This was Mount Merapi’s biggest lava flow since authorities raised its danger level in November, said Hanik Humaida, head of Yogyakarta’s Volcanology and Geological Hazard Mitigation Center.

Authorities in November had evacuated nearly 2,000 people living on the mountain in Magelang and Sleman districts on Java Island but most have since returned. There has been no new evacuation.

The alert was being maintained at the second-highest level and authorities told people to stay out of the existing 5-kilometre (3-mile) danger zone around the crater as the local administrations in Central Java and Yogyakarta provinces closely monitor the situation.

The 2,968-meter (9,737-foot) 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.