- People have been warned not to approach Mount Aso
- A layer of volcanic ash coated buildings, streets and cars in the area
Mount Aso, which stands 1,592 meters (a little over 5,200 feet) tall, is in Kumamoto Prefecture on the southwestern island of Kyushu.
Images from the area showed a layer of volcanic ash coating streets, roofs and vehicles. No injuries have been reported, the Japan Meteorological Agency said.
It raised the alert level for the area to 3, with 5 being the highest level, and warned members of the public not to approach Mount Aso and to beware of falling rocks.
"It is extremely rare for an eruption column to exceed 10,000 meters," Makoto Saito, director of the agency's Volcanology Division, told CNN affiliate TV Asahi on Saturday.
Saito added that while the volcano is in its active phase, there is a "possibility" another eruption of the same scale could occur.
Mount Aso previously rumbled into life
in September last year.
Japan, which sits on the Pacific "ring of fire", has scores of active volcanoes. Level 3 alerts have also been issued this year for the Sakurajima and Kuchinoerabujima volcanoes, according to the Japan Meteorological Agency.