A census carried out in the Virunga Massif - where most of the world's mountain gorillas live - revealed 480 individuals living in 36 groups.

Conservationists say that, 30 years ago, only 250 gorillas survived in this same area.

Along with the 302 mountain gorillas from a census in Bwindi in 2006, the world population is now more than 780.

The Virunga Massif includes three contiguous national parks: Parc National des Virunga in the Democratic Republic of Congo, Volcanoes National Park in Rwanda and Mgahinga Gorilla National Park in Uganda.

The only other location where mountain gorillas exist is Bwindi Impenetrable National Park in Uganda.

A 2003 census estimated the population in Virunga at 380 individuals - so the current figure suggests that the population has increased by just over 25% in the last seven years.

Conservationists say the increase is thanks to that a collaborative "transboundary" effort by organisations in the Democratic Republic of Congo, Rwanda and Uganda to protect the gorillas and their habitat.

But, according to the African Wildlife Foundation and International Gorilla Conservation Programme (IGCP), the animals are still very much under threat.

A joint statement from the two organisations reported that a recent five-day patrol in the Virunga Massif discovered and destroyed 200 poachers' snares.

Poachers typically do not target mountain gorillas, but the snares they set are a still a threat.

Director of the IGCP Eugene Rutagarama said: "Collectively, we cannot let down our guard on the conservation of these incredible animals.

"While mountain gorillas are physically strong, they are also incredibly vulnerable."