Expanding palm-oil plantations in Malaysian Borneo are rapidly eating into the habitat of the rare proboscis monkey and causing its numbers to decline sharply, officials warned Wednesday.

The reddish-brown primate, which is named for its distinctive large and fleshy nose, is found only on Borneo, a large island divided up between Malaysia, Indonesia and Brunei.

But rapid loss of its native habitat in mangrove swamps and jungles, along with poaching, have caused populations in the Malaysian state of Sabah to drop and now just 6,000 exist in five major populations, a statement by Sabah's wildlife department warned.

The number of monkeys in one major population was declining by 10 percent per year, it added.

"I am concerned about the decline in the proboscis monkeys. The report by the wildlife department is alarming," Sabah state tourism, culture and environment minister Masidi Manjun told AFP.

"The proboscis monkey has achieved iconic status and its popularity among tourists can be compared to the orangutan."

The wildlife department said planting of palm plantations along mangrove riverbanks was the key culprit in the monkeys' decline.

Environmentalists say palm plantations are one of the greatest threats to rainforests in countries like Malaysia and Indonesia -- which account for 85 percent of world production of palm oil, an edible oil derived from palm fruit.

Virgin forests are often cleared to make way for palm plantations that stretch to the horizon in many parts of the two countries.

However, Masidi said expansion of other types of farmland was also to blame.

Masidi said state authorities had been ordered to tighten protection of the monkey's habitat.

He added "sufficient land" existed elsewhere in the state for palm cultivation and he hoped the state's official warning on the monkeys would lead to public pressure on "culprits" to cease activities that harm the animals.