Familes across the North Island have been warned of a measles outbreak after at least 10 people contracted the disease following a hip-hop event in Sydney.
Public health officials have warned people who attended the World Supremacy Battlegrounds in early December - and anyone else who has come into contact with them - to look out for symptoms of the infectious disease.
The first confirmed case was a young Auckland woman, and nine other cases in Turangi and Taupo have since been confirmed.
Four of those who have contracted the disease were at the event, and the others came into contact with them.
As extended families travelled around the country over Christmas, officials fear they have spread the disease more widely than would usually be the case.
They have since been in contact with people in Wellington, asking them to stay isolated until they can be cleared of the disease.
Nobody has yet been admitted to hospital but all those infected - ranging in age from five to 28 - have been isolated.
New South Wales health authorities have also confirmed three measles cases in connection with the event, issuing a public warning on Tuesday after an Adelaide competitor became ill.
Public health staff in New Zealand are interviewing people who attended the event, checking whether they were immunised or infected, and have been getting in touch with anyone with whom infected patients have been in contact.
Auckland's last major measles outbreak, in 2011, resulted in nearly 500 cases and 80 hospital admissions, and this is the city's first case since June 2012.
Ministry of Health acting deputy director of public health Harriette Carr said any outbreak was significant because it was New Zealand's goal to become measles-free.
However, the latest outbreak was not yet an epidemic.
"It's highly infectious, and the problem with measles is that people are infectious for five days before they get the symptoms . . . people are giving it to other people before they know they've got it."
Identifying and isolating people until measles could be ruled out was important to stop it spreading, as the number of cases could multiply quickly, she said.
There was a perception that measles was a mild disease, but she warned it could be very serious for those who were vulnerable, such as babies and the elderly.
New Zealanders born before 1969 are likely to have been exposed to the disease as children, and are considered immune.
However, Dr Carr said those born after 1969 and before big pushes to improve measles immunisation rates were at risk.
"It's very important if people have symptoms of measles that they seek medical advice.
"Because measles can be easily spread, however, it's also important that people contact the Healthline 0800 number or ring their doctor first, so that their symptoms can be initially assessed without risk of infecting others in a GP waiting room or hospital emergency department."
She said the latest outbreak was a reminder that the most effective protection against measles was immunisation.
"I think the message is, if you haven't been immunised, it's a good new year's resolution."
MEASLES: WHAT IS IT?
An easily spread, severe viral infection of the respiratory system, passed on by coughing and sneezing.
Symptoms include high temperature, sore eyes and runny nose; small white spots developing inside the mouth; harsh, dry cough; reduced appetite, aches and pains; diarrhoea and vomiting; red blotchy rash developing three or four days after initial symptoms, usually starting on the head and neck.
Children are usually miserable for about a week before recovering.
In some cases measles can cause fits, encephalitis (brain inflammation), hepatitis (liver infection) and pneumonia (lung infection). It can become serious in pregnant women, people with weakened immune systems, and babies.
Anyone with any of the above symptoms should contact their family doctor or call Healthline on 0800 611 116 as soon as possible.
Call before visiting the doctor because measles is easily passed on. Stay away from work, or public places, and from family members if they are not fully immunised.
- Fairfax Media
Should NPDC sell its Tasman farms?Related story: Tasman farms in black