New Zealand could be facing a measles epidemic, with about a quarter of children under the age of five at risk of catching the disease, immunisation experts say.
Notified cases of measles rose to 93 in July, up from seven in June.
Total notified cases this year stand at 133 - more than seven times higher than the total number of cases last year.
Auckland University's immunisation advisory centre is warning further cases are likely as the disease spreads north from the South Island. Researcher Nikki Turner said New Zealand potentially faced a serious measles outbreak.
"We could be seeing the beginning of an epidemic."
New Zealand's measles immunisation rate is among the lowest in the developed world, with 15-20 percent of children not vaccinated before beginning primary school, Dr Turner said.
About 70,000 children under the age of five were at risk of catching the disease as a result, she said.
Measles is highly infectious, with one case able to infect a further 12-18 people. It can lead to hospitalisation, pneumonia and death.
Parents should be aware of the symptoms of measles and ensure children are immunised against the disease, Dr Turner said.
"The only way of preventing measles is by having high immunisation rates."
New Zealand's most recent measles epidemic was in 1991. There were seven deaths from a total of 7000 cases.