A second South Island measles case has been confirmed, with health officials saying a diagnosis in Marlborough is likely linked to a case in Milford Sound.
A third potential case has been isolated in Te Anau.
People with measles are infectious for around 10 days.
The Milford Sound case was announced on November 20, and authorities have since tried to track everyone that patient - a 30-year-old woman - may have come in to contact with.
The woman was the first measles case in New Zealand since May.
In October 2017 the World Health Organisation declared New Zealand had achieved endemic measles elimination status, meaning at least 95% of people were fully vaccinated against the disease.
The few cases of measles since have mostly been imported from overseas.
Measles can be life threatening: about 1 in 10 people with measles will need hospital treatment.
Southern DHB, Medical Officer of Health Susan Jack said the Marlborough patient was a woman in her 20s
"She has been in isolation in Marlborough since Tuesday November 20 . . . we are reasonably confident that she would not have passed the virus on to anyone else in that time.''
None of the three patients are thought to have been vaccinated against measles.
Public health agencies across all South Island DHBs were on the alert for measles cases, Dr Jack said.
