US, NZ to fund Cook Islands port for deep sea mining

The US and New Zealand will jointly fund a port development in the Cook Islands that's expected to pave the way for deep sea mining.

The $US60 million ($A84 million) project is both a rebuke to China's ambitions in the Polynesian nation and a sign of renewed interest from Washington DC.

The deal was signed on the sidelines of the Pacific Islands Forum in Palau on Tuesday by representatives from the three countries.

US Deputy Secretary of State Christopher Landau - alongside NZ Foreign Minister Winston Peters and Cook Islands Prime Minister Mark Brown - said the port would help realise "the enormous potential" of deep sea mining.

"These are minerals that are very important to economic development around the world," he told journalists.

"We look forward to working with the Cook Islands how they wish to proceed with the development of this resource and we look forward to partnering with them with responsible and effective development."

Deep sea mining, which is yet to be commercialised anywhere in the world, involves the extraction of avocado-like nodules from the sea bed.

The practice is deeply controversial and faces pushback from ecologists and conservation-minded governments in the region, who describe it as unproven.

The Cook Islands, under re-elected leader Mark Brown, has been an enthusiastic proponent of the potential industry, which remains in an explorative phase.

The $US60 million commitment will see the Penrhyn port, a former military site and the Cook Islands' northernmost port, upgraded, also providing improved transport links

Mr Brown said the project would build economic diversification and resilience.

Mr Peters, who has championed US investment in the region, said it was a red-letter day for his "quiet diplomacy".

The 81-year-old foreign minister, who has close ties to the Trump administration, has previously criticised the US for its inconsistent diplomacy in the Pacific.

The announcement also appears to draw a line under long-running tensions between Rarotonga and Wellington.