A magnitude-5.7 quake struck off Okinawa in southern Japan on Monday, the Japan Meteorological Agency said, but no tsunami warning was issued.
The quake took place at a depth of 40 kilometres.
Just minutes before the Okinawa earthquake, the northern island of Hokkaido was rattled by a 5.5-magnitude quake at a depth of 220 kilometres in the Pacific Ocean.
Authorities there also did not raise an alarm over a possible tsunami.
There have been no reported casualties or damage in either quake-hit region.