One day when he was very young, he hid in the bottom of his brothers' boat in order to go out fishing with them. Once out at sea, Maui was discovered by his brothers, but they were not able to take him back to shore as Maui made use of his magic powers, making the shoreline seem much further away than it was in reality.
So the brothers continued rowing, and once they were far out into the ocean Maui dropped his magic fishhook over the side of the waka. After a while he felt a strong tug on the line. This seemed to be too strong a tug to be any ordinary fish, so Maui called to his brothers for assistance.
After much straining and pulling, up suddenly surfaced Te Ika a Maui (the fish of Maui), known today as the North Island of New Zealand. Maui told his brothers that the Gods might be angry about this, and he asked his brothers to wait while he went to make peace with the Gods.
However, once Maui had gone his brothers began to argue among them selves about the possession of this new land. They took out their weapons and started pounding away at the catch. The blows on the land created the many mountains and valleys of the North Island today.
The South Island is known as Te Waka a Maui (the waka of Maui). Stewart Island, which lies at the very bottom of New Zealand, is known as Te Punga a Maui (Maui's anchor), as it was the anchor holding Maui's waka as he pulled in the giant fish.
Source: The New Zealand Encyclopedia 4th Edition - Batemen
P.S.: Check out our Auckland Maori Culture Tours including New Zealand Marae Visits in Auckland and Northland.