An immunisation centre at Auckland University says low vaccination rates in New Zealand mean almost 70,000 children under the age of five are at risk of catching measles.
Confirmed cases of the disease have jumped from seven in May and June to more than 80 in July.
Dr Nikki Turner from the centre says about a quarter of children under five could be vulnerable to catching measles.
She says one case of measles can infect a further 12 to 18 people and an epidemic will occur if enough people in a community are not immune to the disease.
Dr Turner says one person in every 1000 cases will die of measles.