Three volcanos in Indonesia are under close watch following heightened activity.
Indonesia's Centre for Volcanology and Geological Hazard Mitigation raised the alert on Mt Anak Krakatau to the second-highest level on Saturday after showers of ash.
The volcano is about 130km west of Jakarta. It formed gradually after Krakatau erupted in 1883. Officials are also monitoring Mt Kelud in East Java and Mt Soputan in North Sulawesi.
Mount Krakatau volcanic activity has increased over the past three days, prompting authorities to raise its status.
The volcano had produced 20 tremors and released 80-meter to 200-meter-long white-grey smoke plumes every hour from Oct. 24 to Oct. 26, Sigin, a monitoring officer , said Friday.
Normally, the volcano produced only five tremors per hour but since last Wednesday the frequency of tremors had increased, he said. Consequently, tourists and fishermen had been warned not to come near the volcano.