Mount Aso, a tourist destination on the main southern island of Kyushu, sent plumes of ash 3.5 kilometers (2.2 miles) high when it erupted at about 11:43 a.m. Japan time, the Japan Meteorological Agency said.
It raised the alert level for the volcano to 3 on a scale of 5, telling people not to approach, and warned of a risk of large falling rocks and pyroclastic flows within a radius of about 1 kilometer (0.6 miles) around the mountain’s Nakadake crater.
Local police said there were no reports of people injured or missing as of Wednesday evening, and that 16 people who had gone hiking on the mountain earlier in the day came back safely.
Television networks broadcast images of a dark cloud of ash looming over the volcano that swiftly obscured large swathes of the mountain.
Ash falls from the 1,592-meter (5,222-foot) mountain in the prefecture of Kumamoto are expected to shower nearby towns until late afternoon, the weather agency added.
Mount Aso had a small eruption in 2019, while Japan’s worst volcanic disaster in nearly 90 years killed 63 people on Mount Ontake in September 2014.