A new survey shows Africa's critically endangered mountain gorillas have exceeded 1,000 after conservation efforts, making them the only great ape in the world considered to be growing in number.

The WWF says mountain gorilla numbers have increased to 604 from an estimated 480 in 2010 in the Virunga Massif, a hilly area encompassing parts of Rwanda, Uganda and Congo.

Combined with the latest published figures from the gorillas' only other home, Uganda's Bwindi Impenetrable National Park, the overall population is 1,004.

Ugandan officials say they expect a rise in the Bwindi population when the results of a recent, separate survey there are released.

Mountain gorillas are popular with tourists. The region's population, however, dropped sharply in the past century because of poaching, illness and human encroachment.