Animal welfare charity Humane Society International staff have described what they say are apocalyptic scenes on fire-ravaged Kangaroo Island, in South Australia, where they have set up a base rescuing injured wildlife.

More than a third of 160km long Kangaroo Island has burned. The video and pictures released by the charity’s disaster response team shows a scorched landscape of scarred trees, ash-coloured earth and animal carcasses.

They also show vision of koalas and other animals being rescued, given water, carried to safety in washing baskets and cared for in a temporary veterinary hospital.

Evan Quartermain, the group’s Australian head of programs and manager of the Wildlife Land Trust, a network of 600 sanctuaries across the country, said the damage on the island was hard to describe.

Humane Society International’s Kelly Donithan with a fire-affected wallaby on Kangaroo Island. Photograph: Evan Quartermain/Humane Society International

“It is extremely emotional,” he said in a statement issued by the organisation. “In some places you can’t walk 10 metres without coming across another carcass.”

Erica Martin, the charity’s chief executive, said in a badly hit area that burned a week ago they found one live koala among thousands of dead koalas, kangaroos, wallabies and birds. “The scenes were nothing short of apocalyptic.”

Amid all this death, every time we find an animal alive it feels like a miracle

The severity and extent of the fires, concentrated in the island’s biodiversity-rich western region, have prompted ecologists to express grave fears for the future of some of Kangaroo Island’s unique and endangered wildlife.

They are particularly concerned for the Kangaroo Island dunnart, a mouse-like marsupial endemic to the island, and the glossy black-cockatoo, a unique subspecies that has been the focus of two decades of community conservation work.

A koala in a burnt forest on Kangaroo Island. The animals that survived the fire risk starving from lack of food. Photograph: Evan Quartermain/Humane Society International

Heidi Groffen, an ecologist with the local Land for Wildlife organisation, last week told Guardian Australia the island was a refuge, or “little Noah’s Ark”, for endangered species.

The fires started with lightning strikes in the Flinders Chase national park. They continue to burn. Two people have been killed, and the farming and tourism industries badly affected.

‘Amid all this death, every time we find an animal alive it feels like a miracle,’ says Donithan. Photograph: Evan Quartermain/Humane Society International

Humane Society International has been working on the island with local groups, including the Kangaroo Island Wildlife Park. Its team is led by Kelly Donithan, a global expert in disaster response. She said the damage to wildlife on the island was some of the worst she had seen.

Donithan said the goal was to keep animals in the wild where possible. “Unfortunately, the landscapes are so decimated that for many this hasn’t been an option because there is nothing left for them to eat or drink, so they need to be taken in for care,” she said.

She said some animals were so badly burned that euthanasia was the only option. “Amid all this death, every time we find an animal alive it feels like a miracle.”