The pact -- seen as an attempt to counter Beijing's rising Pacific influence -- is expected to be signed by leaders Anthony Albanese and James Marape on Wednesday in Port Moresby.

It comes as the Pacific nation celebrates 50 years of independence from Australia.

"Each Party recognises that an armed attack on either of the Parties within the Pacific would be dangerous to each other's peace and security and the security of the Pacific," it states.

Both parties, it adds, declare they will "act to meet the common danger, in accordance with its constitutional processes."

"The parties, respecting the sovereignty, independence and territorial integrity of each other, commit to the mutual defence of each other," reads the document seen by AFP.

The agreement, known as the Pukpuk treaty, commits the two countries to the "integration and interoperability" of their militaries, the treaty says.

The deal also enables nationals from the two countries to serve in each other's militaries.