Vulcanologists in Japan warn that levels in the magma chamber beneath Mount Sakurajima are rising again and another large lava eruption cannot be ruled out.
The volcano in the south of the country has been erupting constantly since 1955.
The ABC reports about 5000 islanders live below the volcano and another 600,000 in the city of Kagoshima, 8km away.
Recently, the volcano discharged more than 100,000 tonnes of ash 5km into the air. Yellow-brown fog fell across Kagoshima on 18 August, transforming day into night.
Sakurajima's last big eruption was in 1914. The ABC reports it was the most powerful in 20th Century Japan - quite an achievement in an archipelago with 108 active volcanoes.
Lava flows filled the strait separating the volcano from the mainland, forming a peninsula. Even though most of the islanders had fled, about 60 people were killed and 3000 houses were burned to cinders.
"The magma level deep within the volcano is back to about 90% of what it was before the 1914 eruption," said vulcanologist Masato Iguchi who has studied Sakurajima for 30 years.
"So we do have to worry about a big eruption in the long term."