New Zealand has agreed to a $NZ2 billion replacement for its ageing surveillance planes, bringing its fleet closer in line with Australia's and pointing to greater cooperation.
NZ Defence Minister Ron Mark on Monday confirmed his government would be replacing its six Lockheed P-3K2 Orions planes with four Boeing P-8A Poseidons.
The new aircraft would provide "a maritime patrol capability with the significant range and endurance needed to assist our partners in the region", he told reporters in Wellington.
The change will cost $NZ2.35 billion ($A2.18 billion) and the Poseidons will be delivered and begin operations from 2023.
Australia has also committed to buying 15 of the planes, which are capable of not just finding, but hunting, submarines.
Analysts say the purchase signals New Zealand's willingness to keep in touch with its traditional allies and show its seriousness about military deployments in the region.
"If you wanted a defence capability that was good for our alliance with Australia ... then the P-8s would be one of your first choices," strategic studies professor Robert Ayson of Victoria University in Wellington told AAP.
Canberra is thought to have been keen on New Zealand also buying the P-8As due to the benefits running similar planes would have on joint operations.
Earlier reports suggested it was raised when Prime Ministers Malcolm Turnbull met with counterpart Jacinda Ardern last year.
"You can, of course, have interoperability without having to operate the same platform, but it helps," Lowy Institute senior fellow and maritime security expert Euan Graham said.
"It's a down-payment on New Zealand's continuing ability and political will to plug into a US-led maritime coalition."
New Zealand's government last week released its long-term defence outlook, flagging concerns about China's activities in the Pacific for the first time, and Dr Graham said the new planes would gave New Zealand options in decades to come.
"It is true China is really the only scenario in which those high-end maritime war-fighting capabilities [of the P-8A] make sense," he said.
The final decision was delayed until Monday due to a change of government last year, with the new defence minister saying he wanted to look over the previous administration's work before proceeding.