One further measles case has been confirmed, and more are expected, as health officials continue to monitor families exposed to the disease.
The latest case, in the Taupo and Turangi area, brings the total to 11, all of whom attended or had had contact with someone who was at the World Supremacy Battleground hip-hop event in Sydney in December.
The outbreak is contained to Auckland, Taupo and Turangi so far, but families in Huntly, Hamilton and Wellington are also being monitored.
Three cases have also been confirmed by health authorities in New South Wales.
Bay of Plenty and Lakes District medical officer of health Neil de Wet said public health nurses had been in touch with more than 50 people over the past 48 hours to check on their risk of catching the infectious disease.
"There are nine that are potentially susceptible, that are not immunised, and we're asking them to stay in isolation. I wouldn't be surprised if we had more cases."
Dr de Wet said the focus was now on preventing the spread, and anyone who had been in contact with people who had been to the Sydney hip-hop event should call a doctor.
"From a public health perspective, this is a very infectious illness and, although the vast majority of people will make a full recovery, about 30 per cent get complications including things like pneumonia, ear infections and diarrhoea."
About one in 1000 people who contracted measles in New Zealand died but, as with any outbreak, the number of people potentially exposed increases and that meant the rates of complications and mortality also rose, he said.
Those who have measles are interviewed to see who they have been in contact with, and those people in turn are checked.
Anyone born before 1969 is considered likely to be immune, as are those who have had the MMR - measles, mumps and rubella - vaccine, introduced in 1990.
But those vaccinated in the 1970s and '80s may be at increased risk, as there is uncertainty over the effectiveness of the shots they received, depending on the age at which they received them and the way the vaccine was stored.
Anyone found to have been in contact with an infected person, and who is unsure of their vaccination status, is being given a blood test to check for antibodies. Anyone found not to have immunity is asked to stay in isolation for 10 days to see whether symptoms develop.
Medical officer of health Stephen Palmer said that anyone who did not have immunity and had been in contact with one of the measles cases had reasonably high chances of developing symptoms.
"It's passed by coughing and sneezing. Just by passing the case on an aeroplane or a bus, people just walking past the case, who haven't even had close contact or don't even know the case, can get it."
A team of 12 from Huntly College competed at the Sydney event and principal Tim Foy said he was working with teachers who accompanied the group to track down the students and inform them of the outbreak and of public health advice.
Mr Foy, who found out about the outbreak yesterday, said he was not aware that any member of the group had contracted the infection.
In June 2012, the Ministry of Health reported that 93 per cent of 2-year-olds had had all vaccinations, including their first of two scheduled MMR shots.
- The Dominion Post
Is New Zealand's airport security stringent enough?Related story: Risky objects bypass Wellington Airport security