Five people in Hamilton have been hospitalised with measles as the number of confirmed cases in the city has risen to 60.
The disease has continued to spread in Hamilton and while still largely associated with Fraser High School, there was also a confirmed case at both Hamilton Girls' High School and Hamilton Junior High School.
Waikato District Health Board medical officer of health Dr Anita Bell said it was investigating around another 14 suspected cases throughout the city.
"It's important that with the spread outside of the Fraser High School community, that people make themselves aware of the signs and symptoms of measles and to check their child's immunity status," she said.
Those at risk included people younger than 45 years old who had not had two doses of the measles-mumps-rubella (MMR) vaccine or had not had a laboratory confirmed positive measles result.
Children over four years old who have not received their second dose of MMR and infants under the age of 15 months who have not received their first routine dose of MMR vaccine were also at risk.
"They are susceptible and rely on everyone else to be immune so that measles does not spread to them," Dr Bell said.
"Measles can be a very serious illness, with one in three sufferers experiencing complications such as ear infections, pneumonia, bronchitis or diarrhoea.
"While one in 10 on average requires hospitalisation, admission rates in this outbreak have been higher."
Immunisation was the best protection from the potentially serious disease, Dr Bell said.
Anyone displaying measles symptoms, including fever, cough, blocked nose and sore red eyes should immediately telephone their doctor or Healthline on 0800 611 116 for advice.
Families were advised to call their doctor before visiting if they suspected someone had measles to avoid spreading the disease while waiting, Dr Bell said.
Measles is spread by tiny droplets in the air and is one of the few diseases that can spread so easily to those nearby.