"Primates in Peril" was released in Madagascar on Thursday with input from 50 of the world's top specialists from the International Primatological Society, Conservation International and other organisations.

Dwindling patches of rainforest and pressure from hunting have brought some species' numbers down to a few dozen, it said.

"If you took all the remaining individuals from the 25 primate species on this list and gave them a seat in a football stadium, they'd all fit," Russell Mittermeier, president of Conservation International, told Reuters.

The report urges immediate action to curb the destruction by farmers and loggers of forests in which primates dwell and end the trade in bushmeat and exotic medicines from animal parts.

"If we do nothing ... as many as one-quarter of all today's primates will be dead within 20 years," it says.

Primates are "relentlessly hunted for their meat and fur, bodies broken for dubious medicines, shot for stealing crops in fields which were once their home".

Of the four global regions inhabited by primates, their situation is worst in Madagascar, where loss of habitat to traditional slash-and-burn agriculture has left some lemur species, such as Perrier's sifaka, stranded in tiny areas of forest.

More than half of Madagascar's lemurs are on the verge of extinction.

The golden-headed langur of Vietnam and China's Hainan gibbon are down to a few dozen. The Horton Plains slender loris of Sri Lanka has been spotted only four times since 1937.

Despite declining numbers, however, no primate species went extinct in the last century.

"Amazingly, we've managed to get through the 20th century without any primate species going extinct," Mittermeier said. "I'd like to think this is partly because of better conservation efforts."