I've found a site which details theories and evidence supporting visitors to New Zealand prior to the Maori and Morioris. Click on "radical" when you get there, to read about how prior visitors may have included:

The Phoenicians c 666BC Mauryans c 240BC Ptolemaic Greeks c 180BC The Celts c 300 The Arabs c 790 Waitaha c 850 Tamils c 1170