Australian citizens and permanent residents can enter for as long as they like.
Passport holders from Andorra, Argentina, Austria, Bahrain, Belgium, Brazil, Brunei, Bulgaria, Canada, Chile, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, Iceland, Ireland, Israel, Italy, Japan, Korea (South), Kuwait, Latvia, Liechtenstein, Lithuania, Luxembourg, Macau, Malaysia, Malta, Mauritius, Mexico, Monaco, Netherlands, Norway, Oman, Poland, Portugal, Qatar, Romania, San Marino, Saudi Arabia, Seychelles, Singapore, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Taiwan, United Arab Emirates, United Kingdom(6 months), United States of America, Uruguay and Vatican can visit for up to 3 months visa free.
Unless you are Australian you will have to apply for an NZeTA. It costs NZ$9 if you use the NZeTA app or NZ$12 if you apply online. You will also need to pay a Tourism Levy of NZ$35.
New Zealand immigration
New Zealand embassies