A strong 6.0-magnitude earthquake struck off Japan's southern island of Okinawa early on Friday, the US Geological Survey said.The quake struck at 4:19 am (1919 GMT Thursday), 165 kilometres (105 miles) northwest of Okinawa's capital Naha at a depth of 138 kilometres, according to the USGS.
There were no immediate reports of casualties or damage.
Around 20 per cent of the world's most powerful earthquakes strike Japan.