State vulcanologist Surono, who goes by only one name, said Friday that authorities decided to raise the volcano's alert to the second-highest level after a spike in activity.

Though there has been no official evacuation order, residents and hikers have been told to stay away from the peak of the 2,430-metre-high mountain.

Indonesia is prone to seismic upheaval due to its location on the so-called Pacific 'Ring of Fire,' an arc of volcanoes and fault lines encircling the Pacific Basin. It has hundreds of active volcanos. -- AP