Wellington: New Zealand has agreed to a $2 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.

A US-made P-8A Poseidon surveillance plane

The new aircraft would provide "a maritime patrol capability with the significant range and endurance needed to assist our partners in the region", he said.

The Poseidons will be delivered and begin operations from 2023.