The latest outbreak follows one that started in Northland last month.
The outbreak on the Bluebridge Cook Strait ferry was on a Picton to Wellington sailing from 2pm-5.30pm on October 3.
Several of the current cases are connected to the ferry ride but health officials had been worried because they did not know who the original ferry case was.
They have now confirmed 'patient zero' was from Northland.
Health New Zealand public health specialist Matthew Reid told RNZ they have been doing genetic testing and interviewing passengers.
Reid said there are eight known cases in the country - in Auckland, Nelson, Northland, Manawatū, Wellington and Taranaki.
Health NZ is warning the sailing was a measles high-risk exposure event with the potential for the disease to spread across New Zealand.
Public Health medicine specialist Sharon Sime told RNZ's Morning Report programme today they were assuming the worst.
She said that anyone who was on that ferry and has measles symptoms, or even if they had measles symptoms which have now resolved, should contact Healthline or their health provider.
Bluebridge Ferry had assisted in providing passenger contact details to health officials to allow them to send out text messages and emails to passengers, she said.
But that did not include all passengers on that ferry as some people booked through other agents.
On Thursday health officials named a Nelson cafe, public toilet and supermarket as locations where people may have been exposed to measles over a three-day period.
Symptoms of measles
The first symptoms of measles are similar to other respiratory illnesses, such as a cold, Covid-19 or flu (influenza) which means it can be hard to know you have the disease, Health NZ says.
Symptoms of measles are: fever (a temperature of at least 38°C), cough, runny nose, sore, red eyes and a rash.
The rash develops three to five days after the other symptoms. It appears as pink or red spots or bumps which start on the face before moving down the rest of the body. The rash may be more difficult to see on darker skin. It is not usually itchy and can last for a week or more.
Get vaccinated before travelling
The Ministry of Health is asking travellers to get vaccinated before they go overseas.
Director of Public Health Corina Grey said there are active outbreaks in several countries popular for New Zealanders to travel to including Australia, Canada, the United States and India.
An overseas link of the current cases in New Zealand has not yet been established. But previous outbreaks have been from non-immune travellers bringing the disease back with them from overseas, Grey said.
Doses of the MMR vaccine prevents 99% of people from getting measles, she said.
