The Department of Sustainability and Environment was last week forced to end the lives of eight eastern grey kangaroos on industrial land north of Craigieburn Road East.

Their deaths followed the euthanasing of eight kangaroos at the same property days before.

DSE senior wildlife officer Glenn Sharp said it was not yet known what illness had hit the kangaroos, but it was necessary to put the animals down to end their suffering.

"Unfortunately, these kangaroos have suffered serious illness and distress," Mr Sharp said.

"Now that the animals have been euthanased, we will be ordering comprehensive post-mortem examinations to determine the cause of their conditions. We now await the post-mortem results and the findings of the EPA, with the aim of preventing more illness among this group of kangaroos."

The department will now focus on determining the cause of the illness.

Most of the dead kangaroos have been taken to Melbourne University for post-mortem examinations, while some are undergoing post mortems at Healesville Sanctuary.

Mr Sharp said the full toxicology results could take up to a fortnight.

The decision to euthanase the kangaroos was made after an assessment by Healesville Sanctuary veterinarians, who are considered experts in Australian wildlife.

The eastern grey kangaroos were shot by a specialist shooter under the supervision of department officers.

The Environment Protection Authority is supporting the department's investigation.

shane.worrell @fairfax.com.au