Australia and Papua New Guinea will be legally obliged to defend each other from a military attack on either territory under a landmark defence treaty, the ABC can reveal.

The agreement will also give the Australian Defence Force unimpeded access to a series of designated facilities and areas within Papua New Guinea.

PNG's cabinet endorsed the high-level security pact yesterday, on the eve of the country's 50th anniversary of independence.

The deal, which is expected to be signed tomorrow, will be known as the Pukpuk Treaty — referring to the Papua New Guinean pidgin word for "crocodile".

"The treaty is meant to prepare our militaries to be battle-ready and for a very bad day," a PNG cabinet submission seen by the ABC said.

"It has the ability to bite and like a crocodile, its bite fo

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