Prime Minister Anthony Albanese will leave Papua New Guinea without a hoped-for defence pact between the two nations, after PNG's cabinet couldn't sign off on the landmark agreement in time.

Mr Albanese and his PNG counterpart James Marape were expected to ratify a treaty deepening military co-operation on Wednesday, but only managed to sign a communique laying out the wording of the pact.

It's an embarrassing setback in Australia's mission to win friends and influence in the Pacific, and marks the second time in as many weeks the prime minister has failed to wrap up a security deal with a Pacific nation amid geostrategic competition with China in the region.

If the treaty is signed next week, the Pukpuk Treaty, named after the pidgin word for crocodile, would elevate the two nations' r

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