A low-decile primary school in Northland has more than 200 unimmunised children, and the region's DHB head, Nick Chamberlain, says it has contacted the board asking for help.
It comes as the Northland district health board is asking schools to consider excluding children who have not been vaccinated for measles.
Dr Chamberlain said school boards of trustees and principals should discuss whether to exclude unimmunised children for at least the next two weeks.
He told Morning Report he has asked schools to write to parents, asking them to consider keeping their children at home.
"Parents then have to make that decision. Obviously most parents are acting in their child's best interests and wouldn't want to be putting their children at risk," he said.
The first two cases of measles appeared in Northland in the holidays, and if more appeared, the high-risk period could be longer.
Dr Chamberlain said the immunisation rate in Northland was about 85 percent, the lowest in the country.
"[I'm] really concerned that those 15 percent who are unimmunised are very vulnerable to what is a deadly disease."
He said a primary school has contacted the DHB saying it has more than 200 unvaccinated children and is asking for its help to get them immunised.
The anti-vaccination movement has targetted the region in recently years, he said, and some parents were choosing not to get the children immunised.
"We had [an anti-vaccination] movie which was shown early last year and was targeting Northland in a big way - it started off in Northland and it was shown many, many times throughout Northland."
Dr Chamberlain said if unimmunised children caught measles there was a 95 percent chance they would spread it to others.
Those at risk include other unvaccinated children, those being treated for cancer and the elderly.
He said he would understand if schools thought exclusion was too harsh.
But he said at the very least, unvaccinated children who were unwell, with a fever, cough or cold must be kept away from school because they could be in the early stages of the measles.
Excluding unimmunised children is 'common sense' - Northland principal
Tai Tokerau Principals' Association president Pat Newman told Morning Report his school was the one with the more than 200 unimmunised children.
But he said it was not known at this stage whether they were all unimmunised, or whether parents had lost the vaccination documentation.
The school was working though the data it had and cross referencing it with DHB data to check, he said.
Mr Newman said excluding unimmunised children was "common sense" and he supported it.
"If, at the end of the day, parents won't immunise their children we have no choice.
"The parent has the right to say 'no', but the school has the legal right to say, under the direction of the DHB, 'I'm sorry, your child will have to stay at home'."
But he said he hoped that this would not need to happen and parents' would show "common sense".
The school was considering methods such as setting up the school hall to put unimmunised children for the next two weeks.
DHBs need to do better on immunisation education - Health Minister
Health Minster David Clark told Morning Report he was "deeply concerned" that vaccination rates have slipped.
He said district chief medical officers have powers to exclude people from schools in a large breakout of a disease, and he would be getting more advice from officials on this today.
But he said he was not sure that banning children was the best approach, and better education, getting out into the communities and onto the marae would help.
"My view is if you punish children for the decisions of their parents you end up entrenching the problem rather than actually [solving] it."
But Dr Clark said the DHB needed to do better and increase immunisation rates in the region.