Rare and endangered northern bettongs have been found in far north Queensland in an area where it was believed the animal had died out, environmental group WWF says.

The northern bettong is one of northern Australia's rarest marsupials and its numbers have dramatically dropped in recent decades.

For more than 10 years, the only place they were known to exist was Lamb Range, south-west of Cairns.

WWF northern bettong project coordinator Jess Koleck said three bettongs had been photographed by a sensor camera in Mount Lewis National Park near Port Douglas, north of Cairns, in an area about 75 kilometres north-west of Lamb Range.

The bettongs were detected in a two-square-kilometre section of the national park.

"After searching for a year and a half, and walking for hundreds of kilometres in rugged bush, this was our eureka moment," Ms Koleck said.

"It means we don't have all our eggs in one basket. If a major fire or disease outbreak greatly reduced the Lamb Range population, there are at least some survivors to the north."

The newly discovered population is thought to be small, but WWF believes more work needs to be done to accurately determine its size.

It is collaborating with James Cook University and the Queensland Government on the project, establishing more than 100 cameras in the wild to search for the creatures, which have an average body length of just over 30 centimetres and weigh only around 1 kilogram.

The northern bettong colony at Mount Lewis is about 75km north of Lamb Range. ( Supplied: Google Maps )

The five-year monitoring program also involves cage trapping bettongs to estimate the size of their population.

Cameras have been placed about a kilometre apart in rows with baits containing peanut butter, oats, vanilla and truffle oil placed nearby, as truffles make up a large part of the animal's diet.

"Looking through a mountain of images has been a slow and tedious process, but we were all celebrating when there on the screen were northern bettongs from three different camera points," Ms Koleck said.

"With only about half the photos sorted from this site, we're hopeful of finding more, but it seems likely their range up in the north is pretty small."