Although New Zealand possesses a very lengthy coastline in proportion to its area, it is not well endowed with natural harbours. In the North Island, Auckland and Wellington are the only two safe natural harbours of which the fullest commercial use can be made. On the east coast of the North Auckland Peninsula several deep and sheltered harbours exist, but as the surrounding country is comparatively undeveloped they are of little economic consequence at present. In the South Island the Marlborough Sounds and the West Coast Sounds form perfect land-locked harbours, but owing to their situations and to the rugged nature of the terrain they have, with the exception of Queen Charlotte Sound, little or no commercial utility. Where vital localities have not been endowed with ideal harbours, it has been necessary to improve existing facilities by dredging and breakwater construction. In this manner efficient ports capable of accommodating overseas vessels have been formed at Lyttelton, Otago, and Bluff.

On the west coast of both islands the strong ocean drifts and high seas cause shoaling at river mouths and harbour entrances, while on the east coast of the South Island similar circumstances prevail due to the large quantities of shingle brought down by rivers being spread along the coast by ocean currents. The mountainous nature of the country makes the haulage of goods to and from the better-equipped natural harbours both costly and difficult, and the construction and maintenance of further ports at various points along the coasts of both islands has been necessary either by dredging river mouths or by harbour construction work.

In the early history of New Zealand, ships were the main form of transport of passengers and goods from one part of the country to another. The development of the railway and roading systems of New Zealand has gradually reduced the volume of coastal shipping, which has now also been encroached on by air transport. The volume of the coastal cargo trade is nevertheless still substantial and there is no sign yet that its days are numbered. Known developments in air transport are unlikely to displace shipping between New Zealand and overseas ports.

Of the numerous New Zealand rivers few are of sufficient length or volume to be navigable; moreover, owing to the high relief of the country, they are mostly swift flowing, while nearly all are obstructed at their mouths by bars. For the purpose of internal communication, therefore, they are of little economic utility and only in two or three isolated instances have they been thus consistently used. With improved roading conditions their traffic has become negligible even in these cases.

The Bay of Islands was the first New Zealand port used by commercial shipping, but port development soon followed in other northern harbours such as Hokianga, Mangonui, and Auckland. Wellington came later, followed by New Plymouth. With settlements becoming established in the South Island, shipping was next recorded at Nelson, Akaroa, and Port Chalmers. By 1853, 11 ports were receiving shipping direct from overseas. The number of ports in use by overseas vessels increased during the goldrush period of the sixties, but later decreased to a number which has not changed greatly during the past 50 years.