Health officials said a 56-year-old woman who had recently returned from Europe tested positive days after completing a compulsory two-week period of managed isolation.
Contact tracing efforts are under way, and authorities have published a list of locations the woman visited.
New Zealand has been widely praised for its response to the pandemic.
The country, with a population of five million, has recorded 1,927 confirmed cases and 25 deaths over the course of the pandemic.