Australian environmentalists say hundreds of koalas have been killed at a blue gum logging plantation in the state of Victoria, sparking an investigation by officials.

"Hundreds of koalas were found dead and injured by locals in the area who tipped us off yesterday," Anthony Amis, a koala researcher for environmental group Friends of the Earth Australia, said Sunday.

"They found koalas bulldozed. Our local sources told us they could smell rotting koalas. It's a massacre," Amis told dpa, adding the incident occurred during logging activities at a timber property near Portland in south-west Victoria over the past few months.

Local Portland resident Helen Oakley, who was one of the first ones to raise the alarm, posted a video to Facebook on Friday, saying she had seen the marsupials lying dead at the site. "Mothers killed and their little babies. Australia should be ashamed of this," she said.

The deaths at the plantation come after tens of thousands of koalas were killed in the bush fires that have burned more than 12 million hectares of land in Australia, including dozens of koala habitats. The fires have put the iconic animals at risk of being listed as "endangered."

Unlike in New South Wales and Queensland, koalas are not a threatened species in Victoria. In fact, in some areas, there are too many koalas, giving rise to issues like not enough food.