The North and South Islands are about to be officially christened after the New Zealand Geographic Board discovered they had no formal names.
The board said it would consult the public and iwi on what each island should officially be called.
For several years the board had been investigating Maori names for the islands and exploring a process for formally recognising alternative Maori names for each island.
Board chairman Don Grant said "While researching this issue, we noted that 'North Island' and 'South Island' are actually not official names under our legislation, despite their common long-term usage.
"We therefore want to formalise alternative Maori names and, at the same time, make the naming of the North and South Islands official."
Alternative naming meant that either the established English names or the Maori names could be used individually or together.
This differed from dual naming where both names were used together in official documents, such as maps.
The alternative names would allow the board to recognise the historical and cultural importance of traditional Maori names, while still retaining the long-term and commonly used English names, Dr Grant said.
The Maori names Te Ika a Maui for the North Island and Te Wai Pounamu for the South Island appeared on early official maps and documents.
Te Ika a Maui translated as "the fish of Maui", based on the Maori myth that the island was formed by Maui's gigantic catch, and Te Wai Pounamu as "the place of greenstone".
The board's research also showed that Maori names for the islands appeared on the earliest maps and charts, including those of Captain Cook.
The existence of several known recorded Maori names for each island meant a lot more work was still to be done to establish the most appropriate names, he said.
Maori leaders warmed to the board's decision, saying it cemented common Maori names and their traditional meaning in legislation.
Te Runanga o Ngai Tahu chairman Mark Solomon said Maori place names were "repositories of traditions and stories of the areas they represent" and that "the tribe supports the reinstatement of traditional place names".
Academic Ranginui Walker told TV3 there was nothing wrong with the English titles, but they were "mundane [and] lacking in imagination".
Maori Language Commissioner Erima Henare said the title Te Ika a Maui was already commonly used, but he welcomed the board's decision to make it official. "It is a bold move, but not before its time."
He said there would be little contention about the Maori titles for the islands, as Te Ika a Maui and Te Wai Pounamu were overwhelmingly the most recognised.
Mr Solomon said that the common use of Te Wai Pounamu did not preclude the discussion of other names. He said that it was important the views of other iwi were sought.
But Wanganui mayor Michael Laws, who was holding a referendum to decide the most preferred name for his town, said the geographic board's decision was "crazy" and culturally biased.
"Where else could you go in the world and the locals have actually two different names for everywhere?
"It is political correctness of the worst kind - unthinking, unfeeling and completely immune from any heritage and history that is not Maori."
The geographic board expected to be able to publicly consult all New Zealanders on the names in 2010.
Historical Maori names:
Te Ika a Maui and Te Wai Pounamu
* Top and Bottom
* Transit and Visit
* Hot and Cold
* Minor and Major
* East and West
* Fush and Chups
* Kiri and Te Kanawa
- additional reporting by NZPA