A rare freshwater turtle species may soon become extinct because of a mystery virus in the population on the NSW mid north coast.

Sick and dying Bellinger River snapping turtles have been washing up on the banks of the Bellinger River, near the town of Bellingen, since mid-February.

The virus attacks the turtles' internal organs, leaving them blind and starving, and most survive only a few days.

So far more than 300 have died as the virus travels upstream.

It is estimated there are only a few thousand of the snapping turtles within the river system.

The National Parks and Wildlife Service (NPWS) has set up an incident management team to manage the situation, and try and save the species.

Deputy Incident Controller Geoff Ross said no turtles had survived the illness.

"It has 100 per cent mortality," Mr Ross said.

"There is no chance any turtle that has this disease has survived."

Scientists try to identify turtles resistant to virus

NPWS staff have been working with vets from Taronga Zoo and across the country to try and identify the pathogen and find a cure.

Mr Ross said very little was known about it.

"We're still looking for that intelligence," he said.

"We're doing a lot of planning to try and conserve this animal and reduce the impacts of this disease on other animals."

Josh Maher says a rebreeding program is needed to save the Bellinger River snapping turtle. ( ABC: Tom Lowery )

Turtles displaying some resistance to the illness have been captured, marked and released back in the river for monitoring.

It is hoped they may be key to stopping the spread of the virus if they can survive.

Local ecologists, however, have called for more urgent action to ensure the future of the species.

Fauna management specialist and local resident, Josh Maher, said a rebreeding program needed to be launched.

"I definitely think it should be happening, and sooner rather than later at the rate this thing is spreading," he said.

He said the healthy turtles which remained in the river may not be enough for the species to recover.

"Even if the animals at the very top end of the river system were to survive, to repopulate the rest of the river could take 100 years, if it were to happen naturally," he said.