The largest known population of rare grey-shanked doucs has been discovered in a remote part of Vietnam, raising hopes that the endangered monkeys can be saved from extinction.

Considered one of the 25 most endangered primates, the species has only been recorded in the five central Vietnamese provinces. Fewer than 1,000 are believed to still exist, and until now, only one other population with more than 100 animals was known.

"This is an exciting and important discovery because of the large size of the population," said Barney Long, a conservation biologist with the World Wide Fund for Nature's Vietnam programme.

"It's very rare to discover a population of this size with such high numbers in a small area, especially for a species on the brink of extinction," he said. "This indicates that the population has not been impacted by hunting like all other known populations of the species." Three surveys since 2005 by WWF and Conservation International in Que Phuoc Commune in Quang Nam province recorded at least 116 animals. To date, only a small part of the area has been surveyed, so there may be significantly more doucs living in the adjacent forest.

Ben Rawson, a biologist for Conservation International's Indo-Burma programme, said: "We now have a much greater opportunity to overcome the very serious threats faced by this species and prevent its disappearance from our planet."

The grey-shanked douc, Pygathrix cinerea, was first described in 1997. They are colobine monkeys with faces that look as if they have been painted orange and cream, with black hands and tufts of grey on their heads. They spend much of their time in treetops, eating fruit and leaves.

Like many primate species in Vietnam, their populations have been devastated by hunting and to a lesser degree by habitat loss.