"To the best of our knowledge there is no warning system there," Carolyn Bell, a USGS spokeswoman, told AFP. "There are none, not that the USGS is aware of.

"Now there may be some local ones, but it's not into a big network that we don't know about," she said. "It's one of these tragic things that make these hazards which we can't stop into disasters which hopefully technology will start to reduce."

The USGS spokeswoman said creating a tsunami warning system for the region would be a challenge.

"This crosses so many countries and so many boundaries in that part of the world and the warning system would have to be so geographically diverse," she said. "We're talking about educating people to what the warning means, what you have to do.

"They're transient, they live in small villages, these things don't happen every day," she said.

Bell said the USGS supports the tsunami warning system in the Pacific but "of course this earthquake was not in the Pacific Ocean."

She said there have been numerous aftershocks since Sunday's quake, which had a magnitude of 8.9, including some registering over 6.0 and 7.0 on the Richter scale.

Some of the aftershocks are some distance from the epicenter of the quake, which was located under the sea off the west coast of northern Sumatra.

"The plate itself is 1,000 kilometers (600 miles) long, the fault right there," Bell said. "It's on a plate boundary.

"Usually the aftershocks, they say geographically, are within a radius of the epicenter but this one was such a huge, huge epicenter and a huge quake that the aftershocks are not next door," she said.

Sunday's earthquake and tsunamis killed thousands in at least seven countries in southern and southeastern Asia. Indonesia, Sri Lanka, India and Thailand were among the hardest hit.

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