According to Indonesia’s geological agency, Anak Krakatoa had been showing signs of heightened activity for days, spewing plumes of ash thousands of metres into the air.
The volcano erupted again just after 9:00 pm on Saturday, the agency said.
Indonesia is one of the most disaster-prone nations on Earth due to its position straddling the so-called Pacific “Ring of Fire”, where tectonic plates collide.
Most recently in the city of Palu on Sulawesi island a quake and tsunami in September killed thousands of people.
On December 26, 2004 a tsunami triggered by a magnitude 9.3 undersea earthquake off the coast of Sumatra in western Indonesia killed 220,000 people in countries around the Indian Ocean, including 168,000 in Indonesia.