Hundreds of kangaroos have been found dead in far west New South Wales from what has been described as a "mystery disease".

Despite good feed and plenty of water around during the last few months, something undetectable has been knocking the roos off.

Former NSW Department of Primary Industry veterinarian in Broken Hill, Greg Curran, who has worked in the region for more than 30 years, said the signs were similar to large macropod deaths he saw in the 1990s and in 2010.

"The epidemic started late last month [September] and early this month," he said.

"It was predictable and the reports we're getting are that people might be seeing five to 10 animals and some people are seeing 40-50 animals.

"If they're seeing that, it suggests there could be between 100-500 dead in any particular area."

Unknown disease has been killing kangaroos in north west NSW. ( Cherie von Hörchner )

The reports have come from the far west of New South Wales, north of Broken Hill up to Tibooburra, across to the Paroo, and have typically featured animals either dead or languishing due to unexplained phenomena.

"Animals appear disorientated," Mr Curran said.

"They're not running off the road but towards vehicles, and kangaroos in paddocks are finding it difficult to move even though they are in good condition."

Similar conditions to previous mass die-offs

Mr Curran said he knew kangaroo deaths were imminent, as weather conditions were similar to those that accompanied mass mystery die-offs in previous seasons, when it was estimated hundreds of thousands of roos within two-week periods.

"We had a chance to look at the disease in detail back in 1998 and again in 2010," he said.

"We've got some understanding of the pathology, but we don't know what the agent is.

"All the work we've done says it's not a plant poisoning and it's certainly not starvation.

"It's possible it's an infectious disease process, but so far we haven't been able to pinpoint that."

The sign at the boundary between Central Darling Shire and the NSW Unincorporated Area in far-west NSW. ( ABC News: Gavin Coote )

Mr Curran said he was surprised at the slow response from industry stakeholders, considering an action plan had been developed after the previous mystery death incidents.

"One of the things I'm disappointed about is that, to date, none of the agencies responsible have been able to, or have been prepared to, investigate what's going on with these animals," he said.

Mr Curran said more attention should be given to the deaths, as the implications are concerning not just for the kangaroo meat industry, but the meat industry in general.

"Given that kangaroos are used for meat, it's important we understand what's going on with these animals," Mr Curran said.

"When we've seen kangaroo die offs, we've also seen some problems in livestock too ... diseases we haven't understood."

Carcases left untouched by other animals

Richard Wilson from Yalda Downs Station near Tibooburra confirmed Mr Curran's observations.

He said the way predators stayed clear of the dead roos merely added to the mystery.

"Two things that stood out — there were no younger roos, they were roos that were in good condition and no wounds on them whatsoever," he said.

"They just simply laid down under a tree and died.

"I did go and check on some of them a week later and there were no pigs at them.

"All the wedgies, the crows and the black-tipped kites that normally get into carrion ... nothing had been eating them."

An unknown illness has killed kangaroos in far west New South Wales. ( Flickr: Nicki )

'Some similarities' to 2010 deaths

Deputy chief veterinarian officer at the NSW Department of Primary Industry, Therese Wright, said the department was aware of the marsupial deaths in the region.

"During October, the Department of Primary Industries received reports of approximately 200 red and grey kangaroo deaths," she said.

"There's not a lot to go on."

Ms Wright said it was unclear whether the current deaths are linked to the events in 2010 and 1998.

"There certainly seem to be some similarities," she said.

"But until samples are actually collected from the field and a full investigation is done, that's really just speculation.

"I think that relates to the time of year and the seasonal conditions.

"I certainly understand that in 2010 it was a fairly similar season with fairly good pasture — there'd been rain and there was some standing water, and again it was just largely sort of sudden death with very little signs."

Ms Wright said the department had decided to suspend further analysis into the mystery kangaroo deaths.

"At this point it appears that the deaths have ceased," she said.

"There's been no reports of deaths since mid-October, so effectively the investigation is on hold."