The Victorian Government is investigating after dozens of distressed, injured and dead koalas were found at a blue gum plantation in the state's south-west.

Key points: A triage of four vets are on the ground working with animal rescuers to save the animals

A triage of four vets are on the ground working with animal rescuers to save the animals Plantation companies are required to apply for authorisation to disturb koala populations under the Wildlife Act

Plantation companies are required to apply for authorisation to disturb koala populations under the Wildlife Act Animal Justice Party MP Andy Meddick is at the site and said it was "absolutely abhorrent"

Officers from the environment department are currently on the ground at the timber plantation near Cape Bridgewater.

WARNING: this story contains graphic images

Portland resident Helen Oakley, 63, first raised the alarm with authorities on Wednesday after hiking in the area and finding the dead koalas, some of which had been there for days.

Ms Oakley posted an emotional video on Facebook at the cleared site.

"Australia should be ashamed, they've bulldozed 140 acres down and just killed all of our koalas," she said in the video.

Ms Oakley told the ABC she had found 10 dead koalas at the property since Wednesday and said dozens more live koalas were trapped in two isolated stretches of gum trees on the property.

"Some of them have been fairly decomposed so they've been there for a while."

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She said she counted 70 to 80 koalas in trees that were still standing.

"But we're finding them in the rows of pushed up blue gums [on the ground], sitting there — I found one yesterday with a broken arm."

Department of Environment incident controller Andrew Pritchard said 25 koalas had been euthanased so far and that about half of the 120 koalas on site had been assessed.

Efforts have been focused on helping the surviving koalas.

"They'll be rehabilitated at a later stage," he said.

The department did not have figures on the number of dead animals on the site.

The Australian Forest Products Association has condemned the deaths.

Chief Executive Ross Hampton said those who work in the forest industry are "appalled … at what appears to be a callous act of animal cruelty."

Mr Hampton said it was unclear who bulldozed the trees "with the koalas apparently still in them".

"But it is absolutely certain this was not a plantation or a forestry company."

"We support all those calling for the full force of the law to be applied to the perpetrator," said Mr Hampton.

Another blow to Australian wildlife

Mr Pritchard said it was not unusual to find koalas in a freshly felled timber plantation.

"They let out a high sugar content to their leaves, and koalas are very much attracted to that," he said.

"The difference in this case is there has been a fence constructed around this plantation and the koalas have not been able to move outside that fence."

He said it was not clear whether the koalas were in the trees when they were felled.

"I'm not clear on exactly if that was the case — koalas do move into trees on the ground.

"That's what we're looking into, the details as to how the animals came to be in this state."

He said the Office of the Conservation Regulator was investigating and that penalties applied for killing or disturbing wildlife.

A number of carcasses have been located at the site. ( Facebook: Helen Oakley )

Victoria's Animal Justice Party MP Andy Meddick has been assessing the damage on the ground since Sunday morning.

"It is absolutely abhorrent," he said.

"They have been felling these trees with koalas still in them; they have then been bulldozing these trees into massive piles that run the length of the property.

"We're still going through these fires in East Gippsland — we've lost an enormous amount of animals," Mr Meddick said.

"How could anyone possibly, in the light of that, conduct an operation like this?"

Mr Meddick said there was a triage of four vets on the ground working with animal rescuers in an operation overseen by the environment department.

He said he would be pushing for a full investigation including a parliamentary inquiry.

It was unclear who was at fault, he said.

"What is clear is that animals have been killed in large numbers."

Vets have euthanised 25 koalas at the site after they were found in distress. ( Facebook: Helen Oakley )

Plantation companies must apply for authorisation to disturb koala populations under the Wildlife Act.

They are also required to undertake risk assessments that identify potential hazards to koalas from plantation management operations, including stress, injury, exposure, and death.

Companies are required to develop a department-approved koala management plan in order to protect animal welfare. The process includes checking koalas in trees and on the ground for unusual behaviour.

Mr Meddick said there may have been breaches of legislation, including the Prevention of Cruelty to Animals Act.

"You are not allowed to harass, intimidate, threaten or kill wildlife — that has happened here."

"I can see it with my own eyes."