Warning: Distressing image

The impact of the Australian bushfires on our wildlife appears to be even greater than previously thought.

It's now estimated that about 1.25 billion animals have perished in the fires, which have also killed 25 people, destroyed hundreds of homes and burnt out more than eight million hectares of land.

It was earlier estimated that 480 million mammals, birds and reptiles had been affected by the fires in NSW alone.

The World Wildlife Fund extrapolated the 1.25 billion figure by using the science of Professor Chris Dickman, whose methodology calculates the impacts of land clearing on Australian wildlife.

Watch 'The Latest on Facebook Watch' here

"This heart-breaking loss includes thousands of precious koalas on the mid-north coast of NSW, along with other iconic species such as kangaroos, wallabies, gliders, potoroos, cockatoos and honeyeaters," WWF Australia CEO Dermot O’Gorman said in a statement.

In the video below: Car loads of koalas rescued on Kangaroo Island

Play Video A group of Good Samaritans has driven through fire-ravaged Kangaroo Island, picking up badly burnt furry friends and taking them to nearby wildlife centres. A group of Good Samaritans has driven through fire-ravaged Kangaroo Island, picking up badly burnt furry friends and taking them to nearby wildlife centres.

"Many forests will take decades to recover and some species may have tipped over the brink of extinction.

"Until the fires subside, the full extent of damage will remain unknown.

A dead koala and its joey are seen after bushfires swept through on Kangaroo Island, southwest of Adelaide. Credit: David Mariuz / AAP

"These fires are far from over and have the potential to be the biggest wildfire disaster in the past century."

Professor Dickman, who last week spoke to 7NEWS.com.au, said rebuilding Australian wildlife populations would be a long-term issue.

"There are a lot of people out there helping by going into areas that have been burned to look for koalas and any other native wildlife has been affected," Dickman said.

More on 7NEWS.com.au

"A lot (of native species) will have been undoubtedly very badly affected by these fires."

Hundreds of thousands of sheep and cattle have also been lost in the blazes, with the army sent in to help bury the livestock.

Millions of dollars have so far been raised to help injured wildlife.