Mt. Asama in eastern Japan erupted on Sunday, according to a local media.
The eruption occurred at 7:28 p.m. local time (1028GMT), with smoke reaching about 600 meters (1969 feet) above the mountain, the Japan Meteorological Agency said, according to the local news agency.
The weather agency warned that flying rocks and pyroclastic flows may reach a radius of about a two kilometers (1.2 miles) from the crater.
It added that the alert status remained at level 2, meaning approach the crater should be avoided.
The agency said that it would closely monitor the volcanic activity, citing the possibility of an eruption on a similar scale.