SYDNEY (AFP) - A shallow 6.4-magnitude earthquake hit the southern Indian Ocean on Saturday, US seismologists said, prompting Australia to issue a tsunami warning which was later cancelled.

The US Geological Survey said the quake struck at a depth of seven kilometres at 1110 GMT, almost 700 miles north-west of Australia's Cocos Islands, also known as the Keeling Islands.

There were no immediate reports of damage or casualties, but the Joint Australian Tsunami Warning Centre (JATWC) issued an alert and advised people not to swim in the sea, and to move away from beaches, harbours, marinas and coastal estuaries. Evacuations from the area were unnecessary, it said.

The centre cancelled the warning around three-and-a-half hours later. It had put the quake at a magnitude of 6.6.

The Cocos Islands are located 2750km north-west of Perth in Western Australia.