Two earthquakes, measuring 6.6 and 4.9 on the Richter scale, rocked the northern Japanese island of Hokkaido within a space of 19 minutes on Saturday, but there were no immediate reports of casualties or damage.
The Japan Meteorological Agency ruled out fears of tsunami tidal waves resulting from the quakes which occurred at 9:03 and 9:22 am (0003 and 0022 GMT).
"There may be some minimal change in the sea level but there is no fear of damage," the agency said in a statement following the first quake which was bigger in magnitude.
The epicenters of the two quakes were located close to each other, at a point some 50 kilometers (30 miles) off Cape Erimo on the island's southern tip.
The focuses of the tremors were both 50 kilometers below the surface of the sea, the agency said.