There are about 60 nationalities that are allowed travel to New Zealand, these are called Visa-Free or Visa-Exempt. Nationals from these nationalities can travel/visit New Zealand without a visa for periods of up to 90 days.
Some of these countries include United States, all European Union member states, Canada, Japan, some Latin American countries, some Middle East countries). Citizens from the UK are allowed to enter New Zealand for a period of six months, without requiring a visa.
All the nationals from the above 60 countries, will now require an New Zealand Electronic Travel Authorisation (NZeTA). In other words, it is mandatory for citizens of the 60 visa-exempt countries to obtain an NZ eTA online before traveling to New Zealand.
Only Australian Citizen are exempt, even Australia permanent residents are required to obtain an New Zealand Electronic Travel Authorisation (NZeTA).
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.