TOKYO, March 2 (AFP) - An earthquake of 5.1 magnitude struck off the southern Japanese island of Okinawa on Tuesday, but there was no immediate report of damage or casualties and no tsunami alert, officials said.

The tremor at 5:21 pm (0821 GMT) came at a depth of 27 kilometres (17 miles) in the Pacific and was centred 65 kilometres east of Naha, Okinawa, the US Geological Survey said.

On Saturday, Okinawa, where more than half of the 47,000 US troops in Japan are based, was hit by its biggest seismic jolt in more than half a century when a 7.0-magnitude earthquake struck, triggering minor tsunamis.

The following day authorities ordered large-scale evacuations on Japan's Pacific coast as waves triggered by Chile's massive earthquake hit, but no injuries were reported.