A big-eared bat which was thought to be extinct has been found in a forest in Papua New Guinea, highlighting the unique biodiversity of the developing nation, researchers said Wednesday.

Until the find the bat, or Pharotis imogene, had not been seen in 120 years.

"The species was presumed extinct," University of Queensland researcher Luke Leung said.

Two University of Queensland students caught the female sample of the species in mid-2012 while conducting field work in the Abau coastal district of Papua New Guinea's Central Province.

It did not match any bat known to exist, and was later determined to be the species not seen since the first and only specimens were collected by an Italian scientist in 1890.

Leung said further studies needed to be done to establish whether the animal was one of a small number of mammals endemic to PNG's southeastern peninsula region, or whether it occurred more widely.

"Many of the coastal lowland habitats throughout Papua New Guinea are among the most threatened in the country due to clearing for logging and agriculture," he said.

"And more field surveys of local bat populations could assess the conservation status of the species and inform future strategies to ensure their preservation."

The bat, which has ears about the size of its head, is listed on the International Union for the Conservation of Nature's "Red List" of threatened species as critically endangered (possibly extinct).

Until now the only information on the species comes from the few specimens which were originally housed at the Museo Civico di Storia Naturale in Genova, Italy.

Catherine Hughes, who was an honours student when she and another student captured the bat, said the discovery demonstrated the unique biodiversity of the mountainous Pacific country.

"There's places in PNG which haven't even been travelled to yet by researchers," she told AFP.

"The variety of habitats and ecologies in PNG is just crazy so you can imagine all these species which are tucked away in there and haven't been found yet."