The volcano emitted 11 new clouds of gas and ash and 76 lava trails in the first six hours of Wednesday, the vulcanology office in Yogyakarta, 30 kilometers (18 miles) away, said in a daily report.

The report said heat clouds travelled as far as four kilometers (2.5 miles) down to Kali Krasak river southwest of Merapi.

The volcano's alert level remains on its highest status, the report said.

Twenty-nine 29 lava flows and five heat clouds were emitted in the first six hours of Tuesday.

The clouds, known by locals as "shaggy goats", consist of volcanic gases, ash and dust and reach temperatures up to 500 degrees Celsius (930 degrees Fahrenheit).

In the southern district of Sleman, thick ash from the clouds covered roofs, trees and cars in the Tunggularum area, said Sapto, an official with the district's evacuation agency.

Residents were seen wearing face masks when travelling outside their homes during the hour-long rain of ash, Sapto told AFP.

Scientists have warned that although the magma flow which forms a dome at the peak appears to be weakening, the structure may collapse and spew out millions of cubic metres of volcanic rock and lava.

Merapi's deadliest eruption occurred in 1930 when more than 1,300 people were killed. Some 66 people were killed when it last erupted in 1994.

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