The Meteorological Agency says the Shinmoedake volcano erupted violently several times today, shooting up ash and smoke up to 2,300 metres in its biggest explosion since 2011.
It said some lava was rising from inside a crater at the volcano.
The volcano, seen in the 1967 James Bond film "You Only Live Twice," has had smaller eruptions since last week.
Entry to the 1,421-kilometre-high volcano was restricted.
Japan has 110 active volcanoes.
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