Hundreds of buildings were destroyed by the wave, which slammed into the coast of southern Sumatra and the western tip of Java about 9:30 pm (1430 GMT) on Saturday after a volcano known as the "child" of Krakatoa erupted.
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 vast archipelago nation 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. Tsunamis triggered by volcanic eruptions are relatively rare, caused by the sudden displacement of water or "slope failure", according to the International Tsunami Information Centre.
Unlike those caused by earthquakes, which trigger alert systems, these tsunamis give authorities very little time to warn residents of the impending threat.
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