The list of eligible countries for the New Zealand eTA has not been finalized by the Government of New Zealand. This list will be published over the coming months.
Currently there are a number of nationalities who can travel to New Zealand without a visa for periods of up to 90 days (including the United States, all European Union member states, Canada, Brazil, Argentina, and Japan). Citizens from the UK can enter for up to six months visa free and Australians can stay in New Zealand indefinitely.
Other nationalities, which cannot enter without a visa, can apply for a visitor visa for New Zealand. More information is available on the Department of Immigration website.