The ash rain only lasted two minutes and fell on just one village on the slopes of Merapi, which overlooks the ancient city of Yogyakarta, Edi Purwanto, an official at the Merapi evacuation post, said.

But local officials say it is difficult to predict when the volcano could erupt, and have been warning residents to evacuate.

Another official, Djilal, said an avalanche of rocks rolled down the slopes of Merapi, but caused no casualties or damage because the affected areas were not inhabited.

While the tower of sulphurous smoke over the volcano had risen to 500 metres (1,640 ft) on Friday, the area surrounding the volcano, which killed 70 people in a 1994 eruption and 1,300 in 1930, was bright with sunshine.

Indonesia has already moved more than 600 people away from Merapi, but officials put the total number of residents on and near the mountain at around 14,000, which includes villages in Central Java and Yogyakarta provinces.

Most of those relocated were women, children and the elderly. Some return to their homes near the volcano during the day to feed livestock, local officials say.

Villagers living on the slopes or in the shadows of Mount Merapi say they will stay put until nature gives them a strong signal, or the government forces them to leave. Many fear losing property and livestock if they go.