Japan’s Meteorological Agency says Mount Asama, about 90 miles (145 kilometers) northwest of Tokyo, erupted early Monday.
The agency said volcanic ash fell over a wide area, including parts of Tokyo. TV reports showed neighborhoods sprinkled with the white flakes.
An alert level of three, which urges nearby residents to take caution, was in place for a 2.5 mile (4 kilometer) radius. Alert level four advises residents to prepare for evacuation.
In Tachikawa, a district in the northwest area of Tokyo, farming areas were coated ash but a local official said because it not harvesting season there was no serious damage.