WELLINGTON (REUTERS) - New Zealand has agreed to buy four Boeing P-8A Poseidon maritime surveillance aircraft through the United States' foreign military sales programme, its defence minister said on Monday (July 9).

New Zealand, which is responsible for patrols and rescue missions in a vast Pacific Ocean zone, bigger than Europe, plans to step up its engagement there, in part to counter the rise of new powers such as China.

Defence Minister Ron Mark said the aircraft, intended to replace New Zealand's ageing Orion fleet, would cost NZ$2.34 billion (S$2.2 billion), including training costs, and would start operations in 2023.

"This decision strengthens the coalition government's Pacific reset by providing a maritime patrol capability with the significant range and endurance needed to assist our partners in the region," Mark said in a statement.

In an e-mail, Boeing said, "We are honoured that New Zealand has selected the P-8 as its new maritime patrol aircraft," adding that it would work with the country to help meet its defence and security needs.

Mark signalled the door could be open for more purchases of maritime surveillance technology in a review of capacity due by the end of the year.

"The complementary capability will consider smaller manned aircraft, remotely piloted aircraft systems or satellites, for additional maritime surveillance tasks," he said.

Last month, South Korea's defence procurement agency said it had decided to buy the P-8 Poseidon as it looks to strengthen anti-submarine capabilities against the threat posed by neighbour North Korea's submarine-launched ballistic missiles.

Boeing says 85 P-8 aircraft now operate worldwide.