Japan 7.0 quake strikes off Okinawa

AFP - People in southern Japan on Saturday braced for a possible tsunami after a powerful earthquake struck the south of the country.

The 7.0-magnitude quake was measured at a depth of 22 kilometres (14 miles) and was centred 81 kilometres east-southeast of Naha in Okinawa, the USGS said.

Japan's Meteorological Agency issued a tsunami warning off Okinawa island, Kyodo News reported, after the quake, which was timed at 5.31 am (2031 GMT Friday).

It later downgraded the warning to an advisory.

The USGS initially reported the earthquake's magnitude at 7.3.

Kyodo, citing local police, said there were no immediate reports of any casualties.

The meteorological agency said waves around 10 centimetres (four inches) high reached land around 30 minutes after the quake, Kyodo reported.

Around 20 percent of the world's most powerful earthquakes strike Japan, which lies near the meeting place of two tectonic plates.

Geologists warn that Japan is overdue for a massive and potentially devastating earthquake.

They point to an 87 percent chance that the "Big One" -- a magnitude-eight earthquake or worse -- will strike the greater Tokyo region, home to around 35 million people, within the next 30 years.

The last time a great quake struck the city was in 1923, when the Great Kanto Earthquake claimed more than 140,000 lives, many of them in fires.