A moderate 5.2 earthquake shook some small islands in southern Japan on Monday, but there was no threat of a tsunami, the Meteorological Agency said.
The tremor, which occurred at 2:32 am (1732 GMT Sunday) at sea, jolted some islets in the Okinawa island chain in southernmost Japan, the agency said.
Its depth was some 20 kilometres (12 miles) below sea level in the East China Sea.
The US Geological Survey reported the epicentre as 90 kilometres northeast of the Ryukyu Islands.
There were no immediate reports of injuries or damage to property. Japan experiences 20 per cent of the world's major earthquakes.