Victorian Premier Daniel Andrews has issued a stern message to the owners of land where dozens of koalas died recently, saying it’s not up to them to decide whether or not they have done “the wrong thing”.

At least 40 koalas are believed to have perished and another 80 are in the care of authorities after timber harvesting on private land at Cape Bridgewater, near Portland in Victoria’s south-west.

Vegetation had been removed by contractors at the property before the owner undertook further clearing.

An investigation is underway by the conservation regulator and environment department and the Premier says anyone found to have done the wrong thing will face a “very stern penalty”.

“It’s not for the landowner to be telling people what’s OK and what isn’t, this notion that quote, unquote ‘it wasn’t that bad’, that’s simply wrong,” Mr Andrews told reporters on Tuesday.

“This is a terrible incident, it’s going to be properly investigated and it won’t be for those who have been involved in it to clear themselves.

“If anyone has done the wrong thing and that can be established, then they will feel the full force of the law.”

The situation down at Portland is currently under investigation by the Conservation Regulator and @DELWP_Vic.

If these deaths are found to be deliberate, we expect swift action against those responsible.

No excuses.https://t.co/7mBplH3VD4

— Dan Andrews (@DanielAndrewsMP) February 3, 2020

Environment Minister Lily D’Ambrosio had earlier decried what she described as the “abysmal act,” vowing to prosecute those responsible with the full force of the law.

Plantation hardwood processing company South West Fibre has denied being responsible for the koala deaths, saying it complied with all legal obligations during its works in October.

“Following the work the site was handed back to the landowner in November 2019,” a statement from the company says.

“SWF left an appropriate number of ‘habitat trees’ for the existing koala population and provided details of such in a letter to the landowner noting that the koalas were uninjured and in good health.”

According to the company, the remaining trees have since been cleared.

Industry body Australian Forest Products Association backed the claims from South West Fibre, condemning the “senseless koala deaths uncovered on a private property by a nature group”.

“I’m advised that the operators were so careful that they even took an injured koala which they found during inspection to the vet,” Australian Forest Products CEO Ross Hampton said.

The AFPA plans to conduct its own investigation parallel to that of the state government and confirmed the land was handed back to the owner before Christmas.

The owner of the farm declined to comment.

-with AAP