The latest earthquake occurred early on Saturday morning in the Pacific, off the southeastern coast of Hokkaido island in northern Japan.
The Meteorological Agency said the tremor's focus was located 30km below sea-level, about 750km north of Tokyo. The early morning quake brought to 27 the total number of tremors felt since Friday.
The first tremor on Friday measured 8.0 on the Richter scale and injured 480 people, besides setting off a blaze in an oil refinery.
Most of the casualties were injured by falling furniture in their homes. Up to 40,000 people evacuated their homes, following the tremor.
Japan is vulnerable to earthquakes since it sits atop the junction of at least three tectonic plates, whose gradual movements trigger tremors. A powerful quake in Miyagi, 300km north of Tokyo, injured about 500 people in July.