The Royal New Zealand Navy has added another new ship to its fleet.

Top navy officers were at a formal ceremony in Whangarei today when the first of the navy's four new inshore patrol vessels was handed over by the builders and formally commissioned.

HMNZS Rotoiti will spend the next week on acceptance trials before heading to the Devonport Naval Base in Auckland.

The ship's first commanding officer is Lieutenant Alistair McHaffie, a son of the former chief of navy Admiral Peter McHaffie.

The other three inshore patrol vessels, Hawea, Pukaki and Taupo, are expected to be formally accepted into the navy within the next few weeks.

The four 55-metre, 340-tonne patrol craft are part of Project Protector, the $500 million programme to supply the navy with seven new ships.

The first, the multi role vessel, HMNZS Canterbury, was commissioned in Melbourne in 2007.

The programme also includes two 85-metre offshore patrol vessels.

The inshore patrol vessels will be armed with three .50 calibre machine guns, and will carry out tasks for government agencies including police, customs, the Ministry of Fisheries, the Department of Conservation and Maritime New Zealand.

They will also play a secondary role in New Zealand disaster relief.

The delivery of the two offshore patrol vessels and the four inshore patrol vessels has been delayed due to problems with gear and fittings.