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Ash clouds over the Aso volcano
Photo: ASO CITY HALL / JIJI PRESS / EPA
An ash cloud thousands of meters high has risen over the Aso volcano in southwestern Japan.
Surveillance camera images showed a violent explosion hurling rocks through the air.
Mountaineers were evacuated around the volcano.
There have been no reports of injuries so far, as reported by the Japanese media.
The authorities called for people to avoid the Aso and its surroundings as it emits hot gas.
In addition, caution should be exercised because of "large flying rocks," said Tomoaki Ozaki of Japan's Meteorological Bureau at a press conference.
Last outbreak in 2016
In the past few days, the authorities had already warned of increasing activity on the 1,592-meter-high Aso on the main island of Kyushu in southwest Japan.
The meteorological authority has now announced warning level three on the five-point scale.
This last applied when the Aso erupted in 2016.
Japan is located on the so-called Pacific Ring of Fire and is one of the countries with the highest volcanic activity in the world.
In 2014, an unexpected eruption of the Ontake volcano in central Nagano Prefecture killed around 60 people.
In Europe, the last outbreak of the Cumbre Vieja on La Palma caused a stir.
atb / AFP