At least 25,000 koalas are believed to have died in a horrific wildfire in South Australia that may have devastating consequences for the survival of the species.

The fire on Kangaroo Island, which was considered a koala safe-haven because its population had escaped a devastating chlamydia epidemic, was described as “virtually unstoppable” on Saturday by firefighters.

On Friday, koala rescuer Margaret Hearle told The Telegraph that another important koala population, nicknamed “the gene pool” because of its good health, had been “wiped out” in Crestwood, New South Wales.

Footage filmed by an ABC cameraman in New South Wales on Sunday showed the charred corpses of hundreds of kangaroos and sheep lying by the roadside.

“Sorry to share these images near Batlow, NSW. It’s completely heartbreaking. Worst thing I’ve seen. Story must be told,” he said on Twitter.