Indonesia, Australia warned of tsunami after 7.9 magnitude quake near Sumatra

A massive earthquake of magnitude 7.9 in shallow waters off the west coast of the Indonesian island of Sumatra today prompted tsunami warnings for Indonesia and Australia.

Indonesia's National Meteorolgical Agency issued the tsunami warning for West Sumatra, North Sumatra, Aceh, Bengkulu and Lampung after the earthquake struck hit West Sumatra, North Sumatra and Aceh, an area hit badly by the 2004 Indian Ocean quake and tsunami.

There were no immediate reports of damage or casualties but the shallower a quake, the more likely it is to cause damage. USGS originally put the magnitude at 8.2, and then 8.1, before lowering it to 7.9.

The quake hit at 7.49 pm local time (1.49am Thursday, NZ time), with its epicentre 808 km southwest of the city of Padang, at a depth of 10 km, the US Geological Survey said.

The Joint Australian Tsunami Warning Centre issued a tsunami watch message for a potential threat to the Cocos Islands and Christmas Island.

Australian Federal Police warned people on the Cocos Islands and Christmas Islands to move away from beaches, harbours, marinas, estuaries and rock platforms.

It said no tsunami waves had yet been observed.

If a tsunami is generated, it could affect the Cocos Islands, southwest of Indonesia, after 8.15pm local time (2.45am NZ time) and Christmas Island after 9.30pm local time (3.30am NZ time).

Indonesia straddles the so-called "Pacific Ring of Fire", a highly seismically active zone, where different plates on the earth's crust meet and create a large number of earthquakes and volcanoes.