Mount Io in Kyushu showed renewed signs of volcanic activity on Sunday, the weather agency said, warning of a possible small eruption.
The Japan Meteorological Agency detected a tremor within the mountain, which is 1,317 meters high and has been quiescent since last August.
The tremor is believed to have been caused by the movement of magma and subterranean water. It lasted for nearly three minutes from 9:23 a.m. and a slight crustal deformation was also observed, the agency said.
Volcanic activity was observed at Mount Io, straddling Kagoshima and Miyazaki prefectures, earlier in the month. There were no signs of magma movements or crustal deformation at the time.
The warning comes amid volcanic activity elsewhere in Japan, including eruptions in June at Mount Asama and Mount Hakone, both close to Tokyo, and in May at Mount Shindake on Kuchinoerabu Island, off the coast of Kyushu.