Many of these tribal people are semi-nomadic and subsist on hunting with spears, bows and arrows, and by fishing and gathering fruit and roots. They still cover themselves with tree bark or leaves.

"They are a vital link to our prehistoric past. If they are lost, India and the world lose a bit of their glorious heterogeneity," said Ajoy Bagchi, executive director of the People's Commission on Environment and Development, India, which has worked with tribal groups in the region for years.

"Even a small loss in any of these groups, barring the more numerous Nicobarese, could seriously endanger their survival. We need to immediately do a count on how many of them are alive."

Officials estimate the tsunami triggered by Sunday's earthquake off Sumatra killed about 12,500 people in India. More than 7,000 people are estimated to have died in the Andaman and Nicobar chain of islands alone.

Authorities are still to trying to reach many far-flung isles closer to Indonesia to assess the extent of the damage to the tribes in the archipelago.

Around 30,000 of the more than 350,000 people in the island paradise are from tribal groups.

PALAEOLITHIC PEOPLE

Anthropologists say their biggest concern was five tiny aboriginal tribes: the Great Andamanese, Sentinelese, Onge, Jarawa and the Shompen.

Some like the Great Andamanese are already down to 30 people while others like the Shompen, who live in the southernmost island of Great Nicobar, number between 200-250.

Officials said they expect many casualties among the biggest tribal group in the region, the Nicobarese -- with a population of close to 28,000 -- who live in the southern islands.

"We hear there are many casualties in Great Nicobar. We are very worried about the Shompen who exist only in small numbers and are highly endangered," Bagchi said.

Similar fears were expressed about the 100-odd Onge, one of India's most primitive tribes living in the Little Andaman island, whose numbers have fallen in the past few decades because of contact with outsiders.

"They are true hunter-gatherers. They only hunt for their own consumption. It will be a tragedy if such tribal cultures are lost," Loknath Soni, a social anthropologist of the state-run Anthropological Survey of India, told Reuters from Calcutta.

Little is known about the approximately 200 Sentinelese who have been traditionally hostile to outsiders.

Government records say the Sentinelese are probably one of the world's only surviving palaeolithic people, who almost never leave their island.

But officials said they had little information about state of the smaller tribes after the tsunami.

"We have no accurate information on these tribal groups, apart from the Nicobarese. The other groups are very small," C. Vasudeva Rao, a senior police officer, told Reuters.