Parents of unvaccinated children are being encouraged not to take them in or out of Auckland as authorities try to prevent the measles outbreak from spreading any further.
It comes as more than a thousand students at South Auckland schools are being kept at home to prevent further risk of contamination. Children at one school were being asked to stay away from a nationwide sports tournament next week for the same reason.
The Ministry of Health is warning people travelling to Auckland to make sure they are vaccinated. It says parents should make sure infants aged 12 to 14 months have their jabs at least two weeks before visiting Auckland - even though the vaccine is usually given at 15 months.
Read more: Everything you need to know about measles
The outbreak, which started in January, has showed little sign of slowing this week with the number of confirmed cases in Auckland rising to 731. Of those 501 are in Counties Manukau. A further 144 cases have been confirmed around the rest of the country.
Prime Minister Jacinda Ardern yesterday called for parents to vaccinate their children, saying it was the most important thing that could be done to prevent the outbreak from spreading any further.
Ardern, who said her own baby Neve was up to date with her vaccinations, said she was worried about those who choose not to get immunised.
"My strong advice to anyone is make sure that you are vaccinated, make sure that you're not relying on simply not having contact. The smartest, safest thing to do is to be vaccinated."
In South Auckland, many schools have asked children to stay home if they aren't vaccinated and there is concern about the highly contagious disease spreading further afield ahead of the School Sport NZ's annual winter tournament next week.
About 25,000 secondary school students are due to take part in the tournament, which is held at multiple venues across the North and South Islands.
College Sport Auckland has asked its 110 secondary schools to check the vaccination records of all students before they go.
At Aorere College in Papatoetoe, principal Greg Pierce said about six students had caught measles this year and one case was still "live", forcing the college to send home 20 to 30 students this week.
He has requested health records from all students heading to the winter tournament.
"We will ask them not to go if they are not vaccinated," he said.
"In our junior school more students are immunised than not. Unfortunately it is the opposite in the senior school. This is causing significant challenges in the lead-up to tournament week."
At Manurewa High School, which is at the epicentre of the epidemic, only half its 2000 students were at school yesterday.
Principal Pete Jones said there were 10 confirmed measles cases and four more pending.
"We asked whānau not to send children who were not immunised. We had just over 1000 students in school today," he said. "That's 300 who had already been sent home and another 700 who stayed home today."
James Cook High School, also in Manurewa, has had one case confirmed and another dozen or so "signalled", and asked parents yesterday to keep unimmunised children at home in two classes where students had contact with an affected student at another school.
"I'm assuming we are just a few days or weeks behind where Manurewa High School are," said principal Grant McMillan.
"At secondary school vaccination data is not collected, all we have is citizenship data. So schools are scrambling now to put together lists of who is and who isn't vaccinated."
Ormiston principal Heath McNeil said one of his students was confirmed with measles two days ago even though he was fully vaccinated. But he said the immunisation meant the case was only "mild".
College Sport Auckland chief executive Jim Lonergan said the number of Auckland secondary schools that had at least one measles case was in "double figures",and schools had taken different approaches to next week's tournament.
"What schools are doing, as far as we can ascertain, is that where students haven't been vaccinated they won't be going because we want to minimise any risk," he said.
Garry Carnachan of School Sport NZ, which runs the tournament, said unimmunised students were not banned and it was up to parents to "ensure their students are protected".
Auckland Medical Officer of Health Dr William Rainger said he had asked schools "to know who is and isn't immune, so they know who to quarantine if they get a case during [tournament] week".
"We have not asked schools to leave behind students and staff who are not immune, but we have given clear advice about what they need to do should anyone become unwell," he said.
"We are attempting to strike a balance between the risk of further spread of the disease against the importance of these events in students' lives."