The video filmed on January 28 and uploaded to YouTube on Monday shows the incident unfold to the horror of two concerned women behind the camera.

It is believed the animals were able to escape the fall unharmed.

After several koala deaths in 2013, the Rainforest Alliance temporarily stripped ABP of its environmental credentials.

ABP - Australia's biggest wood-chipping company - last year agreed to employ koala spotters during harvesting and also set a policy to leave at least nine trees standing around koalas found in its bluegum plantations.

Managing director Tony Price said the expanding koala population had increased the chances of similar incidents at Bessiebell, .

"From time to time, occasionally you miss one due to the human factor, but in this case fortunately we're pleased the animal and its young were fine," he told The Standard.

"That's been verified by a wildlife carer.

"Koala spotters were there and an area was marked for a koala but unfortunately in this case they moved.

"Our procedures have improved substantially but as with any procedures we're constantly looking to monitor the performance of them and looking to improve them.

"We have due processes in place and our contractors report all incidents, whether they be actual or near misses.

"We did cease the operation in this instance for a number of reasons."

Koroit wildlife carer Tracey Wilson, who actively campaigns for koala protection, has backed ABP's adoption of new measures as an example for the rest of the timber industry.

"ABP are the only ones spending a lot of money getting spotters on the ground and trying to make a difference," she told The Standard yesterday.

"I believe this was a rare occurrence for ABP but it happens a lot on other plantations.

"We all want the best for koalas but we shouldn't headhunt a company trying to do the right thing."

Mrs Wilson said there could always be more done for koala conservation.

"Even with spotters on the ground it can be difficult to see them, and sometimes they move.

"Other companies aren't going to the same expense for the koala's safety, which indicates this sort of thing is happening on a larger scale."

Rainforest Alliance spokeswoman Anita Neville said the organisation was conducting initial enquiries as required under its complaints investigation protocols.

"We understand that the company that owns the plantation has reported the incident to DEPI and wildlife carers as per their standard operating procedures," she said.

"We also understand that the company has halted harvesting activity on that plantation until its own investigations are completed. These are important corrective actions.

"The Rainforest Alliance treats these matters very seriously and will review the actions taken by the company as part of our ongoing role as an Forest Stewardship Council certifying body."

Friends of the Earth Melbourne notified The Standard of the footage but chose not to comment on the story.

j.pech@fairfaxmedia.com.au