Most harbours with any volume of commercial activity are controlled by harbour boards whose constitution, functions, and powers are set out in the Harbours Act 1950, supplemented by such local Acts as are passed in respect of each board and such general legislation of the country as affects them. A harbour board (other than those whose members are members of a local authority) consists of elected members. One or more members of each board represent one or more constituent districts, with the district represented by the total membership having some relationship to the sphere of influence of the imports and exports of the port. There are 33 harbour boards, 23 of which are autonomous bodies and 10 whose members comprise the members of the territorial locality authority.

Under the Harbours Act the Minister of Marine and the Marine Department are responsible for the administration of harbours where there is no harbour board. Until 1959 the Department operated the port of Picton, and it still carries out the full functions of a harbour board at Westport.

The years since the Second World War have seen substantial development of ports in New Zealand to make good the leeway lost in that period, and to keep pace with the expanding economy and with the increase in size and number of ships, both in the coastal and overseas trades. This development has occasioned healthy rivalry between ports, each seeking naturally its full share of the trade. Since 1945 harbour boards have been authorised to borrow about £40 million for development. As a consequence of the centralisation of shipping during the war, numbers of the smaller ports let their port facilities deteriorate and in the immediate post-war years they found great difficulty in re-establishing the port and the trade, with the result that several of the boards were dissolved. The trend today is for fewer harbours, each, however, equipped with modern facilities to obtain a better turn-around of ships.

A number of the country's non-capital ports are associated with special industries: Tauranga, pulp and paper and log exports; Westport and Greymouth, coal; and Whangarei, oil refinery.