Three cases of measles are confirmed today in an outbreak of the disease in Waikato, the Waikato District Health Board (DHB) says.
Seven cases were suspected and more were likely, it said.
The outbreak appeared to have started about a week ago in Te Awamutu, Waipa, south of Hamilton and its surrounding communities, medical officer of health Dr Dell Hood said.
The DHB had written to parents of children attending schools or early education centres in the area advising them of the outbreak which involved students at Te Awamutu College.
"Because these cases have been in different places in the school holidays, it is very likely more cases will occur ... in other schools and preschools," Dr Hood said.
She urged parents to fully vaccinate their children.
"When measles is circulating, almost everyone who is not already immune to measles will develop the illness if they come into contact with it."
Anyone in contact with a case of measles who was not immune or immunised must stay at home and avoid visitors for 14 days to avoid spreading the illness, the DHB said.
Measles began with a fever, cough, sore eyes, and general unwell feeling. A rash would follow a few days later.
The illness incubated for 10 to 12 days or more.
People were contagious from the start of the illness until four days after the rash had appeared.
Anyone who suspected they had measles should seek medical advice.