A defence treaty with Papua New Guinea would bring the relationship with Australia's closest neighbour even closer, the prime minister says, despite delays in putting pen to paper.

Anthony Albanese is in Port Moresby as PNG marks its 50th anniversary, with more celebrations to take place on Tuesday.

The anniversary is set to coincide with Australia and PNG agreeing to a new landmark security agreement, although it has yet to be formally signed off.

The prime minister said the treaty would be significant.

"This agreement, that's going through the processes here in PNG, will just take that partnership to the next level," he told ABC TV on Tuesday.

"It will be a treaty similar to the relationship that we have with the United States."

Mr Albanese said PNG's cabinet had not signed off on

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