Australia and Papua New Guinea will promise to have each other's backs under a new defence pact named after a dangerous reptile found in both countries - the crocodile.

But signing off on the deal may not be as snappy as Anthony Albanese hopes for because of a hold-up in gaining PNG Cabinet approval for the pact.

The prime minister is in Port Moresby attending celebrations of the 50th anniversary of PNG's independence from Australia and hopes to finalise and sign the new pact on Wednesday.

Mr Albanese told reporters on Tuesday the PNG Cabinet met on Monday night to give final approval but didn't have a quorum because some ministers were back in their constituencies for independence celebrations.

But he expected his counterpart James Marape to sort it out quickly by ushering the process

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