Beginning October 1, 2019, United States & Canadian citizens - along with 58 other nationalities that can currently enter New Zealand under the NZ waiver program - will require an NZeTA (New Zealand Electronic Travel Authority) visa to enter the country both by air or by cruise ship. The eTA visa will be good for 2 years and provide multiple entries into New Zealand.
The following link provides additional information and includes how to apply.
https://www.immigration.govt.nz/new-zealand-visas/apply-for-a-visa/about-visa/nzeta
