It's official - New Zealand's North Island and South Island have alternative Maori names, Te Ika-a-Maui and Te Waipounamu respectively.

Land Information Minister Maurice Williamson says people can use whichever name they prefer and won't be forced to use both of them.

"Everyone will have the choice to keep calling the islands what they always have, or use the assigned alternatives, or use both together if they wish," he said on Thursday.

His decisions are in line with recommendations from the New Zealand Geographic Board.

The board undertook lengthy public consultations, inviting submissions and talking to residents from both islands.

Te Ika-a-Maui translates as Fish of Maui - a reference to the legend that the demigod Maui and his brothers fished up the North Island from their canoe. Te Waipounamu means the place of greenstone.

Mr Williamson has also formalised the names North Island and South Island.

"While these names appear in official publications, including maps and charts, they had been recorded names only and had no formal standing," he said.

"It's only right that those names be made official under the New Zealand Geographic Board Act".