The Orang-utans of Borneo are facing an unprecedented threat as their habitat is destroyed to satisfy increasing global demands for bio-fuel.

As jungles are rapidly replaced by palm oil plantations, the great apes starve and are hunted, mutilated, burnt and snared by workers protecting their crops.At a rehabilitation centre run by the charity Borneo Orang-utan Survival, there are more than 600, mostly orphaned babies. Lone Nielsen, the centre's director, estimates that for each of the 227 animals they rescued last year, five more were killed in central Borneo alone.

"There are broken bones, cracked skulls, burns, internal injuries," said Miss Nielsen. "The plantation workers beat them because they want to catch them and the only way you can catch an orang-utan is to knock it unconscious."

Each orphan must be raised to the age of eight by a human "mother" who teaches it to be afraid of rubber snakes and other hazards before it can be released on to an island.

The "children" engage in amusingly human antics - one of them walking with a stick like an old man. In Indonesian "orang-utan" means "forest people" and after humans they are the most intelligent primate.

In 2004 there were 37,000 living on Borneo and the only other wild population is around 7,000 on the neighbouring island of Sumatra. The palm oil crisis struck central Borneo in 2003, shortly after the Indonesian government declared it wanted to become the world's biggest producer.

In 2004 a "master plan" was unveiled to create 40,000 square miles of plantations by 2010. Campaigners say 70 per cent of the plantations will replace existing forests. As the plan is put into effect, each year provides more orang-utan casualties than the last for Miss Nielsen's centre.

With the world desperate for "green" fuels, demand for palm oil, which is used in bio-diesel, is guaranteed to increase. According to European legislation two per cent of all diesel must be vegetable oil, rising to 5.7 per cent in 2010 and 10 per cent by 2020.

But in the areas where palm oil is produced, environmental concerns barely register with government authorities or the companies they licence. Global prices are rising and there is big money at stake.

A common tactic, campaigners say, is for plantation firms to first burn the forest then buy up the degraded land for a pittance.

Moses Nicodemus, the provincial government's chief environmental official, said: "The basis of palm oil development is sensitivity to community and environment."

He denied that plantation companies were responsible for killing orang-utans.