A moderate earthquake hit off southwest Japan late on Saturday but there no immediate reports of casualties or damage, seismologists said.
The tremor hit off southwestern Tanegashima island 1,000 kilometres (620 miles) southwest of Tokyo at 9:58pm (1258 GMT).
The US Geological Survey measured the tremor at 6.1 magnitude with a depth of 21 kilometres while the Japan Meteorological Agency put it at 5.7 and a shallower 10 kilometres.
A massive magnitude 9.0 earthquake and following tsunami devastated northeast Japan on March 11, with nearly 28,000 people dead or missing.
A number of strong aftershocks have shaken the country. A magnitude 7.1 tremor hit the region late on Thursday.