A critically endangered gorilla species in the war-torn Democratic Republic of Congo has lost more than three-quarters of its population and risks disappearing in the next five years, experts warned Wednesday.

Just 3,800 Grauer's gorillas (Gorilla beringei graueri) are left in the wild, according to the study in the journal PLOS ONE, describing the world's largest primates' "catastrophic decline."

Prior to the civil war which broke out in 1996 in the former Zaire, there were nearly 17,000 of these gorillas.

"While we knew that Grauer's gorilla was in trouble nobody had realized how much they had declined," said lead researcher Andrew Plumptre of the Wildlife Conservation Society.

The unrest that erupted in the region 20 years ago has made it hard to count the gorillas, which have been increasingly hunted for bushmeat by armed miners.

These great apes were among two subspecies of Eastern gorillas that were listed as critically endangered on the International Union for Conservation of Nature (IUCN) Red List in September.

The other subspecies, known as Gorilla beringei, has dwindled to 5,000.

Researchers fear that the Grauer's gorilla could be lost from many parts of its range within five years, unless more is done to save them.

Some strategies could include halting mining in protected areas and encouraging the military to protect wildlife, researchers said.