Friends of the Earth said the “koala massacre” came to light when local activists saw bulldozers pushing the bodies of dead koalas into waste piles left over from the main logging operations.
The logging industry group said on Sunday that the forestry contractor who harvested the bluegum plantation in November followed all of the stringent wildlife protocols in place to protect koalas.
The Australian Forest Products Association says the land and its remaining trees were bulldozed after the contractor had left, with the lobby group pledging to hold its own investigation into the incident.
The Department of Environment, Land, Water and Planning confirmed on Sunday morning that it had been at Cape Bridgewater, about 14 kilometres west of Portland, for several days and had rescued a number of animals.
The news comes after many thousands of koala deaths in the bushfires that ravaged the east and north of the state in December and January.
The department said it was prepared to prosecute over the events.
“We are extremely concerned about these reports of a koala population on private land near Cape Bridgewater where animals are showing signs of starvation and injury,” a spokeswoman said.
“The conservation regulator is currently investigating this matter, with the department.
“If this is found to be due to deliberate human action, we expect the conservation regulator to act swiftly against those responsible.”
The departmental spokeswoman said the rescue and recovery operation was set to continue in the coming days.
“Wildlife welfare assessment and triage will continue with qualified carers and vets,” she said.
“[The department] will be onsite ensuring resources and expertise is available to continue to care for wildlife injured.”
Australian Forest Products Association chief executive Ross Hampton condemned those responsible for the koala deaths and injuries.
“All those who work in our forest industries join with the community in appalled shock at what appears to be a callous act of animal cruelty,” Mr Hampton said.
“It is unclear as yet who bulldozed the trees with the koalas apparently still in them, but it is absolutely certain that 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.”
Noel Towell is State Political Editor for The Age