Auckland's public health service is checking in with more than 2000 people who may have been exposed to measles as the number of confirmed cases climbs.
Since Sunday, the number of confirmed cases has risen to 34.
Auckland Regional Public Health Service medical officer of health William Rainger said a further 34 people were in quarantine and they were following up with more than 2000 people who might have been exposed to the disease.
He said figures have doubled from about 17 to 34 in the past 10 days - the first case was reported in February and the numbers spiked up in the later part of April.
"We had a fair proportion of the cases that have been hospitalised this time, almost 60 percent that had to go to hospital. That's quite a high proportion, so it shows us that measles can be a serious disease that needs to be taken seriously," he said.
The last measles outbreak in Auckland was in 2014 from January to June when there were 112 confirmed cases, and in 2011 when there nearly 500 confirmed cases, Dr Rainger said.
Parents are being asked to make sure their children are immunised on time and also check their immunisation history.
The regional public health service said the best protection against measles was to be vaccinated.
Latest figures show 102 confirmed cases of measles across the country.
Measles is a highly infectious viral illness that can lead to serious health complications - including infections of the lungs and brain - and is sometimes fatal. It is easily spread through breathing, coughing and sneezing, but can also spread before the infected person feels sick or shows symptoms.
Symptoms include a high fever, runny nose, cough and sore red eyes.
A rash also appears on the face and neck a few days later, and then spreads to the rest of the body.
Anyone who thought they had measles should call their doctor or Healthline before turning up to a waiting room.
In New Zealand, the MMR vaccine is routinely given to children at 15 months and four years old, ARPHS said.
Dr Rainger said those with measles could potentially infect up to 15 others if they were not immune.
He said parents should also check their child had the appropriate MMR vaccine.
Adults under 50 years who have not had even one MMR dose should also get their free vaccination from their GP.
Those over 50 are considered immune as the disease was widespread in childhood, according to the the public health service.
One MMR vaccine dose protected about 95 percent of the population, with a second dose protecting close to 99 percent.