Small tsunami heading towards Perth

CANBERRA - A small tsunami sparked by a huge earthquake in Indonesia was making its way down the West Australian coast towards Perth, an Australian seismologist said today.

Geoscience Australia seismologist Mark Leonard said the 23cm tsunami had already hit the Cocos Islands, an Australian territory in the Indian Ocean 2950km north-west of Perth.

It was also likely to have reached the North West Cape on the West Australian coast, and would continue to travel south towards Perth.

But he suggested major damage from the surge was unlikely, and the wave would be difficult to detect with the naked eye.

"As we speak there's probably a tsunami of a few tens of centimetres going down the Western Australian coast," Dr Leonard told ABC radio.

"It would have already gone through North West Cape. It's probably approaching Perth as we speak.

"You may, if it's a nice, quiet surf day, see the sea drop about a foot or so," he said.

"It will go up and down over a period of tens of minutes, but you'd have to be watching very carefully to see it."

He said the 23cm tsunami detected this morning by monitoring equipment in the Cocos Islands was significantly smaller than the 35cm wave recorded there following the 9.0 Boxing Day quake that sparked the Indian Ocean tsunami disaster.

The latest quake, measured 8.7 on the Richter scale, struck off the Indonesian island of Sumatra.

Indonesian authorities have said at least 300 people are dead on Nias Island, off Sumatra, with hundreds more feared buries in the rubble.

However, the US Pacific Tsunami Warning Centre has issued a bulletin saying no major tsunami has been detected near the epicentre of the quake.

A Perth Bureau of Meteorology spokeswoman today said it had issued a tsunami alert warning some parts of Western Australia could be affected by the small tsunami.

"At this stage we are looking at a tsunami warning (which) may impact the Western Australian coast," the spokeswoman said.

Dr Leonard said that if a tsunami was going to hit Indonesia it already would have occurred.

"Whatever tsunami was going to hit Indonesia has already happened," Dr Leonard said.

He warned other places though may still be in danger.

" ... Madagascar and places like that, which are probably the most likely place after Indonesia to have any damage, has still got a few hours to go," he said.

- AAP