Australia and Papua New Guinea will commit to defending each other from armed attacks as they face "emerging threats" to their security, a new defence treaty seen by AFP on Tuesday showed.

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.

The agreement, which also enables the nations' citizens to serve in each other's militaries, comes as Papua New Guinea marks 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," the pact states.

Under the treaty, both parties will "act to meet the common danger,

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