In this Jan 29, 2019, photo, Mount Merapi spews volcanic material as it erupts as seen from Cangkringan, Yogyakarta, Indonesia. (SLAMET RIYADI / AP)

YOGYAKARTA, Indonesia — Indonesia's volatile Mount Merapi volcano has unleashed a river of lava that flowed 1,400 meters down its slopes.

The alert level of the volcano has not been raised but people should stay out of a 3-kilometer danger zone around the crater

Merapi, on the island of Java, has entered an "effusive eruption phase," Kasbani, head of the Volcanology and Geological Hazard Mitigation Center, said Wednesday.

Kasbani, who goes by a single name, said the volcanic material that spewed out late Tuesday was the volcano's longest lava flow since it began erupting again in August.

He said the alert level of the volcano has not been raised but people should stay out of a 3-kilometer danger zone around the crater.

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In this Jan 29, 2019, photo, Mount Merapi spews volcanic material as it erupts as seen from Cangkringan, Yogyakarta, Indonesia. (SLAMET RIYADI / AP)

The 2,968-meter mountain, located near the ancient Indonesian city of Yogyakarta, is the most active of dozens of Indonesian volcanoes.

Its last major eruption in 2010 killed 347 people.

Indonesia, an archipelago of more than 260 million people, is prone to earthquakes, tsunamis and volcanic eruptions because it straddles the Pacific "Ring of Fire."