Indonesian authorities have evacuated more than 900 people and are facilitating the safe return of 170 climbers stranded after the eruption of Semeru volcano, one of the country's tallest mountains.

The alert level was maintained at its highest after Semeru on Java island erupted 10 times on Wednesday, emitting massive plumes of ash and sending lava and rocks as far as 13km down its slopes, officials said.

The climbers were stuck overnight at a lakeside camping area at the foot of the volcano about 6.4km from the crater but were now being helped to safety, said Septi Wardhani, an official at Semeru national park.

"All climbers with their guides are safe," Wardhani told Reuters. "The situation is under control,"

Footage from Indonesia's volcanology agency showed a huge cloud of hot ash

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