On-line Te Reo Māori Dictionary

K, consonant, is pronounced as in English. The Ngaitahu tribe, of the South Island, almost invariably replace ng with k. There are a few words with alternative forms, with and without k, as tena, tenaka; aua, kaua. Our present knowledge of the language does not justify the assertion that the difference is one of omission or insertion. In poetry, particles sometimes lose an initial k.

Williams Dictionary