Indonesia has raised the alert for its most volatile volcano, Mount Merapi, to its highest level and warned villagers in threatened areas to move to safer ground.
Officials said activity at the volcano, in central Java, had increased markedly over the weekend.
People living within a 10km (6 mile) zone were told to evacuate.
Mt Merapi last erupted in June 2006, killing two people.
The men died after they sought refuge in a bunker to escape a burning cloud of gas and ash emitted by the volcano.
Officials said about 500 volcanic earthquakes had been recorded on the mountain over the weekend.
"The magma has been pushed upwards due to the escalating seismic energy and it's about a kilometre below the crater," AFP news agency quoted government volcanologist Surono as saying.
An eruption in 1994 killed 60 local residents, while about 1,300 people died in a 1930 eruption.