(CNN) -- The largest population of a "critically-endangered" gibbon species has been discovered in Vietnam, according to a leading conservation group.

A new census of the northern white-cheeked crested gibbon by Conservation International (CI) scientists has found a population of 455 -- living in 130 groups -- in Pu Mat National Park, in the north of the country.

The discovery represents over two-thirds of the total number of the species left in Vietnam, and is the "only confirmed viable-population of this species left worldwide," according to CI.

Russell A. Mittermeier, president of Conservation International says all of the world's 25 different gibbon species are under threat from extinction, but none more so than the white-cheeked gibbon.

"This is an extraordinarily significant find, and underscores the immense importance of protected areas in providing the last refuges for the region's decimated wildlife," Mittermeier said in a statement.

Population data was collected using "auditory surveying" -- a technique which uses the species' loud morning calls -- for identification and to determine group numbers, CI says.

But the remote, high-altitude forests which have fostered the gibbons thus far is under threat from road development which will not only cut through their habitat but also encourage further dangers, say conservationists.

"The major issue will be hunting of these gibbons that were previously protected by the harsh terrain," primatologist Luu Tuong Bach, who led field surveys.

"Without direct protection in Pu Mat National Park, it is likely that Vietnam will lose this species in near future," he added.