Lava flowing from a volcano in the Democratic Republic of Congo is threatening a population of endangered chimpanzees.

Mount Nyamulagira erupted in the early hours of Saturday morning, raining molten rock down on the forest slopes north of the country's eastern city of Goma.

The affected area is deep inside the Virunga National Park, home to a spectacular range of mega fauna including rare chimpanzees, the okapi, and critically endangered mountain gorillas.

Rivers of lava flowing since the eruption appear likely to stop short of the nearest human settlement in Saki, according to park officials, but the eruption has been "very destructive" to the chimpanzee range on the western slope of the vast Nyamulagira volcano.

"It's chimp habitat so it will have an impact," Virunga park director, Emmanuel de Merode, said by telephone from the Congo yesterday.

"The population there was already heavily depleted by years of fighting."

The so-called "Tonga group" of chimps most directly affected by the eruption is estimated to have been reduced to as few as 40 animals prior to the latest threat.

Africa's oldest national park is studded with the spectacular cones of a half dozen active volcanoes whose forested flanks boast some of the richest biodiversity anywhere on the planet.

But it is also home to nightmarish human conflicts, with a series of civil wars and the backwash from the genocide across the border in Rwanda making it one of the most unstable places in the world.

There are several armed militia groups and rebel armies running illegal timber, charcoal and mining trades in North Kivu province.

Believed to be the most active volcano in the world, Nyamulagira erupts every three to four years with the last blast in 2006 covering large areas of forest with thick, black volcanic rock.

Pictures from the current eruption show a curtain of fire sweeping across the dense forest.

There has been no chimp census possible in recent years as the area is too dangerous for park rangers to operate in.

"We know they are there because we can hear them," said Mr de Merode.

"It's a chimp habitat but it's very remote."

The refugee city of Goma on the north shore of Lake Kivu has been haunted by volcanic activity since Nyiragongo, to the immediate south of Nyamulagira, covered the city in lava in 2002.

Its half-million inhabitants are expected to escape the worst of the latest blast.

"I was awoken at 3.45am by a loud bang, which I at first thought was the sound of war," said Innocent Mburanumwe, the warden for the southern sector of Virunga Park.

"Then I saw the mountain was on fire with sparks flying. We could see that we were not in immediate danger here at Rumangabo, but there are many people who live to the south of the volcano, where the lava is heading."

Park rangers had to evacuate their headquarters in 2008 when it was overrun by the forces of renegade general Laurent Nkunda.

He has since been placed under house arrest in Rwanda, but the HQ was fired on again last year by government soldiers angry at attempts by rangers to move against the lucrative charcoal trade.