No future exists for the orang-utan unless concerted efforts are made to save enough habitat to ensure their survival, a British charity warns.
Orang-utan populations are rapidly declining amid devastating forest fire outbreaks, with more than two million hectares of land in Indonesia lost in recent months.
As world leaders have gathered for talks in Paris for COP21, rescuers calling for an end to the fires have released striking images of the animals stranded in burnt-out forests.
The fires that have spread uncontrollably in Indonesia have been exacerbated by an extended dry season, caused by the El Nino weather pattern, experts said.
Despite monsoons giving some respite, there are fears another severe drought next year could see further outbreaks of forest fires, resulting in more orang-utan deaths.
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Workers from International Animal Rescue (IAR), based in Uckfield, East Sussex, have helped rescue more than 20 orang-utans from burnt forests in Ketapang in the past few months.
Tantyo Bangun, chairman of IAR Indonesia, said: "This is by far the largest number of rescues IAR has had to conduct in the area since we opened our orang-utan centre in 2009.
"And it is a terrible and deeply worrying indication of the plight of orang-utans in Indonesia."
IAR said the animals were suffering from starvation and malnutrition as the fires had left behind barren landscapes with few trees and no food sources.
Gail Campbell-Smith, programme manager for IAR Indonesia, said: "The saddest image you can think of is a magnificent orang-utan that should be travelling in the top of the canopy but instead has to drag itself on the ground.
"An extra concern is that, as habitat is wiped out, instances of human orang-utan conflict increase and these orang-utans are in danger of being killed by farmers as they enter farms looking for food."
Karmele Llano Sanchez, program director of IAR Indonesia, said: "This is not very different to the devastating effects of a war and it should be considered a world crime.
"It is vital that serious action is taken to prevent further outbreaks of fires."
