A rare visiting whale in Wellington Harbour has won hearts in the New Zealand capital but forced officials to cancel the city's annual fireworks display.

The southern right whale appeared in the harbour on Wednesday and has delighted onlookers as it blows water spouts not far from downtown office towers.

Whales regularly migrate along the North Island coast near Wellington but do not usually venture into the harbour.

The city's acting mayor, Ms Jill Day, said its presence meant a fireworks display scheduled for today could not go ahead as experts had advised that the pyrotechnics - to mark the Maori new year celebration Matariki - could make the mammal behave unpredictably.

The whale's appearance is trending on Twitter #wellingtonwhale. But it was less popular with the operator of the North and South Islands car ferry service as it prevented the ship from berthing for about 30 minutes.