Jakarta: Mount Slamet volcano in Central Java province erupted again on Friday, spewing a column of ash up to one km high, forcing more than 20,000 villagers living on the slopes of the mountain to prepare for evacuation, officials said here.

Powerful bursts of hot ash and gravel erupted at 12.44 p.m. and 1.35 p.m. Jakarta time from the rumbling volcano, Sutopo Purwo Nugroho, spokesman of the national disaster management agency, told Xinhua over phone.

Mount Slamet has been erupting on and off since days ago, but went on overdrive Friday, he said.