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.
