Mount Aso, one of the world's most active volcanoes, and the biggest in Japan, erupted early on Saturday (8 October), the island nation's Meteorological Agency said. The eruption left a thick column of volcanic ash belching 11,000m (7 miles) into the sky.
The agency issued its third-highest alert – on a scale of five levels – to warn people not to approach the volcano, and restricted entry around the mountain. They also warned of gas and falling rocks after the volcano burst to life at one of the peaks of the 1,592m (5,222 ft) mountain in Kumamoto Perfecture.
According to local media reports, there were no injuries or damages reported immediately as a result of the eruption. It was reported to have begun at 1.46am local time on Saturday (4.46pm GMT on Friday, 7 October).
It is believed to be the first explosion at this particular peak since January 1980, a Reuters report said, although, it was reported that the mountain previously erupted in September 2015 after being inactive for almost 19 years.
"Mount Aso is in an unstable condition and could erupt again on the same scale," Japan Times cited an agency official as saying.
The newspaper reported there was also a small-scale eruption on Friday. But it is unclear if the current explosion was related to a powerful earthquake that hit Kumamoto and neighbouring Oita Prefectures in April, the official said. The disaster killed at least 49 people.
One of the most active peaks in Japan, Mount Aso is also thought to be a popular hiking spot.
Japan, which is home to 100 active volcanoes, lies on the so-called Pacific "ring of fire" where a huge proportion of the earthquakes and volcanic eruptions in the world are recorded.
In September 2014, the country suffered an unexpected volcanic eruption, the worst volcanic disaster in Japan in almost 90 years. Mount Ontake in central Japan's Nagono Prefecture rumbled to life killing 63 people.
Currently, the country is reported to have a dozen volcanic warnings in effect.