PNG

Australian Prime Minister Anthony Albanese declared it was a "great day" for both countries, and said PNG - the only country in the world where rugby league is the national sport - "deserves" a spot in the league.

Some have lauded the pact with PNG - which declared independence from Australia in 1975 - as another major strategic win for Australia.

"Over the past couple of years, with the heightened geopolitical interest and engagement in the Pacific, something a lot of other middle powers and major powers have struggled to do is to get PNG on a deal of exclusivity for security partnerships," said Oliver Nobetau, a PNG government lawyer turned policy analyst at the Lowy Institute think tank.

But their framing does have the effect of eliminating almost every other potential partner - and Mr Nobetau said the announcement could be seen by some in PNG as "an exertion of Australian power over PNG sovereignty".

In exchange, PNG signed a separate pact which it says reaffirms its commitment to Australia as its major security partner.