Mount Oyama on Miyake Island in the Izu Island chain is likely to erupt soon, the Meteorological Agency warned Monday, forcing at least two-thirds of the island's 3,850 residents to evacuate.
The island is about 200 km south of Tokyo.
The warning, which said the volcano could erupt within the next two hours, was issued at around 7:30 p.m. after a series of mild earthquakes shook the area. Such alerts are issued when volcanic activity becomes especially intense and urgent countermeasures are required.