Indonesia's Anak Krakatau volcano in Sunda Strait, straddling East Java and Sumatra, has spewed ash and flaming rocks.
Officials raised alert levels to 'high' on Friday as the volcano showed signs of increased activity, producing 117 small eruptions.
Staff at the observation post in Pasauran, Banten Province are on a 24-hour watch. Residents in Pasauran have been told to stay at least two kilometres away from the volcano.
Anak Krakatau means 'Child of Krakatau', named so because it rose in the place of Krakatoa volcano after it blew itself apart in one of the most destructive eruptions in history in 1883. The area is a popular tourist site and many villagers farm on the slopes of nearby Ibu Krakatau (Mother of Krakatau) on the same island.
"Until now we are still on alert level but when we examined our equipment on October 27 and 28 we experienced tremors," said Anton Priambudi, a volcanologist observing Anak Krakatau.
Several volcanos in Indonesia increased their activities recently following Mount Merapi's eruption on Tuesday.
The eruptions came only a day after a tsunami struck the remote islands in western Indonesia.