The eruptions from the volcano on Kyushu in southwest Japan occurred in the morning, CNN reported. The activity began Jan. 26, the first such in decades, experts said.
In the town of Takaharu, with a population of 1,159 residents, were advised to evacuate as volcanic ash covered their homes, streets and vehicles and caused flight cancellations. Hundreds of people had already fled.
On Tuesday, Shinmoe's eruption was loud enough to shatter windows of homes, forcing residents to sleep in gymnasiums, the report said.
"People in the area should prepare for the worst case scenario," Satoko Ohki with the Earthquake Research Institute at Tokyo University was quoted as saying.
He said in the 1716-1717 eruptions, a huge explosion sent tens of millions of cubic feet of molten rock and other solids through the crater. He could not say if a similar scenario could recur.
Mount Shinmoe was seen as the hideout of the villain in the 1967 James Bond movie "You Only Live Twice," the CNN report said.