Eight hundred years after the Maori first arrived in New Zealand, and 370 years after Europeans spied its shores, the South Pacific nation's major land masses will finally get official names.

For generations, the two main islands have been called the North Island and the South Island. They have also appeared that way on maps and charts. But in recent years, officials discovered an oversight: the islands had never been formally assigned the monikers.

On Thursday, the land information minister, Maurice Williamson, announced that the North Island and South Island names would become official, effective next week. Equal status will be given to the alternate Maori names: Te Ika-a-Maui ("the fish of Maui") for the North and Te Waipounamu ("the waters of greenstone") for the South.

Don Grant, chairman of the New Zealand Geographic Board, said the country had an informal process for naming places before 1946, when the formal process was set up.

He said the Maori names for the islands had been the same since Europeans first arrived, but the English names had changed over time. On some early maps, he said, the islands were called New Ulster and New Munster, after the Irish provinces. The South Island was also sometimes called the Middle Island, a reference to the much smaller Stewart Island, which is even further south.

Grant said the North Island and South Island names became widely accepted after they were endorsed by an MP in 1907. But he said the names never became official, perhaps because there was no controversy or question about them.

At least, that is, until 2004, when somebody challenged the South Island name, saying it should be renamed to its Maori moniker. Grant said that this was when the board first discovered that neither island had an official name.

But there were more delays. After the board studied the issue, a 2008 law change inadvertently prevented places from being given dual names. So the board waited until 2012 when the law was fixed. Then it put the names out for public consultation, Grant said, and a majority of the people who weighed in said they preferred the dual-name approach.

Next Thursday, he said, the names will be entered into the New Zealand Gazette, finally making them official.