Defence Minister Ron Mark said the estimated cost of the Lockheed Martin aircraft was more than $NZ1 billion ($A950 million), although a price hasn't yet been finalised.

He said the military would buy the stretch version of the plane, the C-130J-30 Super Hercules. Lockheed describes the planes as workhorses that are capable of landing on austere runways almost destroyed by natural disasters.

The announcement came as part of a broader 11-year military investment plan of $NZ20 billion that includes spending on new vessels and maritime surveillance.

Mark said the investments were primarily humanitarian in nature, designed to provide assistance and security to New Zealand's Pacific neighbours.

New Zealand's air force currently operates five C-130 Hercules planes, three of which it took delivery of in 1965 and two in 1969. The planes have been upgraded several times since then.

Australian Associated Press