There are now 759 confirmed cases of measles in Auckland, up 28 since yesterday.
Auckland is at the centre of the outbreak with hundreds more cases than the rest of the country combined
The Auckland Regional Public Health Service said the number was 143 higher than this time last week.
It was warning Auckland schools to take serious precautions if they were participating in the many sports tournaments due to start around the country next week.
Anyone with symptoms of measles, including a cough or runny nose, should not be included in teams, it said.
And schools should request proof of vaccination for any student - and parents aged under 50 - who are travelling.
It said though the sports tournaments were important, that needed to be balanced with the risk of spreading measles among students or outside of Auckland.
The New Zealand Director of Public Health, Caroline McElnay, said the country may have lost herd immunity.
That was when enough people were vaccinated to provide a degree of protection to those who were not.