Hundreds of people who may have been exposed to measles have been contacted by health authorities in Auckland.

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There have been 61 confirmed cases of the highly infectious disease nationwide, with another 31 potential cases under investigation around the country.

Auckland medical officer of health William Rainger said its team have quarantined 59 people, and been in touch with another 900 people who may have been exposed to the highly infectious disease.

"The number of contacts that we are dealing with is about 900. Those are people that we have followed up who may have been exposed through waiting rooms or lecture theatres or different events and we provide those people with advice about what to do if they develop symptoms, and to get immunised," Mr Rainger said.

"We've got 59 people who are in quarantine at the moment, so that's people we're asking to stay at home during the incubation period in case they develop measles.

"It's a reasonably large number of people that we're following up at the moment and our objective is to prevent the spread of the virus further in the community."

More than half of the confirmed measles cases are in Canterbury, and nine cases have been confirmed in Auckland, from a one-year-old baby to people in their 40s.

Dr Rainger said health authorities expected more cases of the disease imported into Auckland but it was not yet an outbreak.

"Whether we are going to get sustained transmission from person to person within Auckland, we don't know if that's going to happen yet. That's when numbers would start to go up quickly. We're not in that state at the moment."

Health authorities are doing their best to quarantine people who have had contact with measles to their homes but it is not always possible.

One woman with measles is in isolation, but she was infectious when she visited two supermarkets and a cafe in Silverdale and Orewa last week.

It's been two years since New Zealand was rid of endemic measles for the first time, meaning any new cases are brought in from overseas.

Of the 31 potential measles cases under investigation, five are in Canterbury, another five are in Auckland, and the others are scattered throughout country.

ESR public health physician Jill Sherwood said not all of these cases would be measles.

"Some of those cases will end up being shown not to be measles. When we have outbreaks like we're having at the moment, family doctors tend to be very good about notifying anything that is suspected of being measles," Dr Sherwood said.

"They are requested to do this, it's good practice because it's better not to miss a case."

One of the main factors preventing measles becoming commonplace again, is if 95 percent of the population is immune.

Dr Sherwood said New Zealand's measles immunisation rate was not high enough to stop measles becoming endemic here again.

"The better that the vaccination rates that you are able to put out there, it's a bit like building fire breaks - when there's a fire, the more chances that set of people won't come into contact with people who are not immune and therefore it will die out."

Auckland Primary Principals' Association president Craig Holt said schools in the region were moderately concerned about the measles outbreak.

He said schools were keeping an eye out for any cases of measles.

The Ministry of Education said it had not been notified of any measles cases in Auckland schools, early childhood centres or kura.