Mount Shinmoe in the Kirishima mountain range bordering Kagoshima and Miyazaki prefectures erupted early Wednesday, marking its first such activity in about six years.
The Meteorological Agency raised the warning level for a volcanic eruption to Level 3, restricting entry to the mountain. It warned the volcano might grow more active, as swelling of the mountain was observed.
Volcanic tremors had been intensifying in the area since late September, prompting the agency to raise the warning level to Level 2 on Oct. 5 to restrict entry to areas near the mouth of the volcano. Level 5, the highest alert, urges people to evacuate.