The tsunami was caused by "an undersea landslide resulting from volcanic activity on Anak Krakatau" and was exacerbated by abnormally high tides because of the full moon, one official said.

Scientists say the tsunami could have been caused by undersea landslides from Krakatua erupting 24 minutes earlier.

The Krakatau volcano, which lies in the Sunda Straight between the islands of Java and Sumatra, has seen increased activity since June.