In the first six hours of Thursday, Merapi sent 80 lava trails spilling down its slopes, some reaching down two kilometers (one mile), said Tri Yani of the vulcanology office in Yogyakarta, located south of the simmering peak.

"It is the first time that lava was seen flowing to the west," Yani said, adding that the volcano had also released heat clouds.

The 2,914-meter (9,372-foot) high volcano, which set off alerts in mid-May, had gradually calmed down before reawakening on Saturday following a strong earthquake that shook the region, killing over 6,200 people.

Scientists have warned that the earthquake could increase the threat posed by the smouldering volcano, saying the magma dome forming at the peak may crack or collapse, spewing out millions of cubic metres of volcanic rock and lava.

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