At least 136 wedge-tailed eagles and four other protected species have been found dead after an extensive search of rural properties in East Gippsland of south-eastern Australia.

‘The eagles were hidden throughout property in bushland and scrub - and we believe that numbers may be higher than what we have seized,’ the state of Victoria's environment department said on Tuesday.

‘At this stage, no charges have been laid, but we have someone helping us with our enquiry,’ the department posted on its Facebook page.

Wedge-tailed eagles are a protected species in Australia. They are the biggest bird of prey in the country, and have become a nuisance for many farmers because they target newborn lambs.

Iain Bruce, an official with the environment department, told Australian broadcaster ABC the killing was intentional and could be the worst mass killing of the eagle they have ever seen in Victoria.

‘It's clearly intentional,’ he said. ‘This is the biggest case of wedge-tailed eagle deaths we have ever seen - by far the biggest.’  ‘We have never seen anything like this.’  Bruce said the finding has turned into ‘a significant statewide investigation, involving more than 30 staff.

‘We are throwing everything at this... it's our highest priority,’ he added.

Deliberately killing the wedge-tailed eagle carries maximum penalties of about 8,000 Australia dollars (6,000 US dollars), with an additional fine of 800 dollars for each bird killed, as well as up to six months' jail.