Curator of Pacific Art Crispin Howarth said, "There are only 10 or 15 of these known in the world and this is the most fantastic."

It had "aspects of male and female" to it and was collected in 1959 by an Australian patrol officer, he said.

He has spent the past two years curating Myth + Magic: art of the Sepik River, an exhibition of Papua New Guinean tribal art created for cultural practices in the Sepik River region and including ancestral figures, masks and supernatural beings.

Howarth said the crocodile was carved from ironwood in a Kundima village on the Korewori River, a tributary of the Sepik River and would have taken a team of artists between three and six months to complete, using adze blades, flints and rats' teeth and no metal tools. But while it was the largest single item it was far from the only one in the exhibition.

"There are 85 works, 80 of which were found in different basements and storerooms around Australia," he said.

Many of these were collected during the period in the 20th century when Papua New Guinea was under Australian administration and were never publicly displayed, he said.

The other five items - including the crocodile - were on loan from the Papua New Guinea National Museum and Art Gallery in Port Moresby. They were brought as part of a "twinning" project involving the National Gallery of Australia, the Australian War Memorial and the National Museum of Australia providing assistance to the Port Moresby museum. Two of the latter's long-serving employees, principal technical officer Grace Vele and senior curator Francis Bafmatuk, escorted the items to Australia and were helping to set up the exhibition.

Vele said she hoped Australians would enjoy the Pacific art and that there would be more such exhibitions in the future with artworks travelling in both directions.

Myth + Magic: art of the Sepik River is on at the National Gallery of Australia from Friday, August 7 to November 1. Admission is free.