No serious injuries have been reported since the initial eruption last Wednesday, but public broadcaster NHK said a woman suffered cuts from shattered glass in Tuesday's blast.
NHK said the eruption was five times larger than the initial activity last week, which was Shinmoedake's first major eruption in 52 years.
Japan's Meteorological Agency has restricted access to the mountain, and on Tuesday broadened the no-go zone to anywhere within a 2 1/2-mile (four-kilometer) radius of the crater. Two lodges and scattered homes are within the perimeter.
Dozens of domestic