A Meteorological Agency panel has decided to closely monitor seismic activity under Mount Fuji, Japan's tallest mountain.
The Coordinating Committee for Prediction of Volcanic Eruptions said that while an eruption is not expected in the near future, it will set up a task force to study disaster-prevention plans for people living near the 3,776-meter volcano, 100 km west of Tokyo.
Mount Fuji, sitting on the border between Shizuoka and Yamanashi prefectures, is one of 86 active volcanoes in Japan. It last erupted in 1707.
The decision came after the number of low-frequency earthquakes at the mountain set a monthly record in November, agency officials said.
Experts believe the mild quakes, which can last up to 30 minutes, indicate active movement of underground magma.
The frequency of the mild quakes surged from the normal 10 a month to 133 in October and 221 in November, agency officials said.
The committee, headed by University of Tokyo seismologist Yoshiaki Ida, said an eruption could affect wide areas including central Tokyo.
Mount Fuji sits on the same volcanic belt as Mount Oyama on Miyake Island, which erupted in June. The island is in the Pacific 150 km southeast of Mount Fuji.
Shikine, Kozu and Niijima islands, part of the same island chain as Miyake and sitting on the same underground belt, were hit by a number of earthquakes in the summer and fall.
The committee also said it expects that Mount Oyama will continue to spew volcanic gas for a protracted period of time, adding that there have been no signs of a reduction in volume.
According to one member, around 1 cu. km of gas has been released from the mountain so far.