What may be the strongest earthquake in 40 years has struck off the Indonesian island of Sumatra, Sunday, 7 am local, sparking deadly tsunami waves that have impacted as far away as India. Hundreds have been killed in Sri Lanka, and Thailand. Indonesia is bracing for high casualties, but little is know as telecommunications to northern Sumatra have been cut.

U.S. experts say it is the worst quake in Indonesian history and the fifth strongest since 1900.

The huge temblor, which the United States Geological Survey says measured 8.9 on the Richter scale, hit early Sunday morning in the Indian Ocean - off the west coast of Indonesia's northernmost Sumatra Island.

The earthquake caused a tsunami, or tidal wave, that hit coastal regions as far away the Maldives and including Sri Lanka, Bangladesh, India and Thailand. Hundreds of thousands of people are believed displaced.

The full extent of damage and casualties in Indonesia are still not clear. Telephone communications between Jakarta and the province of Aceh in northern Sumatra have been cut.

Andi Mallararengeng, spokesman for Indonesian president Susilo Bambang Yudhoyono, says details of the disaster are still coming in.

"We got a report that number of victims, eight, nine, more than 20 on different cities in Aceh, like Lhokseumawe, Banda Aceh, Meulahbo, so we don't have complete information yet because the chain of information at localities in Aceh are being damaged. So we are waiting for more accurate information," he said.

President Yudhoyono has instructed civil and military authorities in Aceh to do everything in their power to rescue survivors and help families of the dead.

Aceh has suffered for years from a separatist rebellion and is currently ruled under emergency regulations. The spokesman says that the tens of thousands of troops in the province would be used to assist the victims.

Indonesia sits on the so-called "ring of fire," a highly active seismic band where plates of the earth's crust collide.