About 700 students and staff at a Waikato high school will have to prove they have been vaccinated for measles on Tuesday - or they won't be allowed back on school grounds.

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In a letter sent to parents on Friday, Morrinsville College acting principal Scott Jenkins confirmed a student had contracted measles and the school would be closed tomorrow.

Mr Jenkins said the school would re-open on Tuesday, but only staff and students who brought written evidence they had been given two MMR, or measles vaccinations, would be allowed in.

He said verbal confirmation would not suffice.

Those students and staff who did not have the two required vaccinations should stay at home for at least two weeks, he said, not returning until 24 May.

All sports games were also cancelled over the weekend as a precaution.

Waikato District Health Board said it was dealing with 20 confirmed cases of the measles, with another 12 under investigation.

And a health scholar said small to medium sized outbreaks of measles would continue if people did not get vaccinated.

A professor of health at Otago University, Michael Baker, said despite the latest outbreak, New Zealand is still set to to have eliminated measles by 2020.

"Hopefully that message is also going out to people in the Waikato and throughout New Zealand that it is really critical to get your children vaccinated."