Another 39 measles cases have been confirmed in Auckland overnight as the city teeters on the edge of an epidemic.
Measles has been rapidly spreading after 37 new Auckland cases were also confirmed on Tuesday morning and 126 in the eight days before that.
The total number of city cases this year now sits at 585, Auckland Regional Public Health Service said.
ARPHS public medicine specialist Dr Maria Poynter earlier warned it was a "very serious outbreak".
She urged anyone aged between 1 and 50 years old to make sure they had at least one measles vaccination, given just one shot would protect 95 per cent of people from the disease.
It comes as nine out of 10 people who contracted measles this year had not been vaccinated or didn't know their vaccination status, new figures by Government agency, the Institute of Environmental Science and Research figures, showed.
Children have been hit particularly hard.
There have been 87 cases in 50 schools across the Auckland region since the start of the outbreak as well as 63 cases in 36 early learning services.
Papakura High School is among the latest to be affected, posting a message to its Facebook page confirming a measles case at the school.
The school remained open for vaccinated children, but information has been posted to Facebook advising parents who suspect their child isn't immunised to keep them home and in quarantine until this Saturday.
Poynter said the numbers of children hit by measles didn't reflect just how much disruption the disease was causing.
Every time a person is found with measles at a school, all unvaccinated students and staff members who were in the same class, team or school group as the person must spend one to two weeks in quarantine.
This is because they may be developing measles without knowing it and could infect others, given disease symptoms take 10-14 days to show.
While vaccination records are kept on a national register for Kiwis born since 2005, it can be harder for school staff or overseas-born students to find their vaccination records.
In cases where they can't find their records, they also have to go into quarantine.
"When there is a student In quarantine, parents have to take time off work and a student's learning is affected," she said.
"It also means unvaccinated children cannot play sport, attend parties or school events, or have non-immune visitors, as they may be developing measles."
Despite the pressure, schools seem to have done well putting at-risk children into quarantine and educating their families about the wider risk to the community, she said.
Measles can also make people miserable and really sick and had led to a high rate of people seeking treatment at hospital during this outbreak.
"The vast majority of people would not have had to stay in isolation or quarantine if they had had even one MMR vaccination," she said.
Poynter's comments come as the latest ESR figures showed there had been 639 measles cases nationally since the outbreak began in February.
Of those cases, 354 people were unvaccinated, while a further 216 did not have records of their vaccination status.
Another 22 had partial vaccination, and 47 were fully vaccinated.
Just four district health boards - Tairawhiti, Whanganui, Nelson Marlborough and the West Coast - had not had any measles cases this year.