Ten cases of measles have been confirmed by the Ministry of Health.
One of the confirmed cases is in Auckland and nine are in Turangi and Taupo.
Another case is under investigation in Turangi/Taupo.
The Ministry of Health acting deputy director of public health, Harriette Carr, said the Auckland person and three of the nine confirmed in Turangi/Taupo attended the 2013 World Supremacy Battleground hip-hop competition in Sydney last month.
The remaining cases were family or known to those who had been at the festival. No one had yet been hospitalised but all those who were infectious were being kept isolated at home.
Public health authorities were working to identify people who may have been in contact with those affected, Dr Carr said: "Measles can be a serious disease and is easily spread to someone who is not immunised, or who has not been exposed to measles previously."
Public health unit staff were following up with those who had been in contact with the infected, and emergency departments had been alerted to watch for possible measles symptoms.
"It's very important if people have symptoms of measles that they seek medical advice. Symptoms can include fever, runny nose, and sore, watery red eyes that last for several days before a red blotchy rash appears.
"Because measles can be easily spread, it's also important that people contact the Healthline 0800 number or ring their doctor first so that their symptoms can be initially assessed without risk of infecting others in a GP waiting room or hospital emergency department," Dr Carr said.
The cases were a reminder that the most effective protection against measles was immunisation.
A publicly funded vaccination was available via GPs. People should also make sure their routine vaccinations were up to date before travelling overseas.
Lakes District Medical Officer of Health Dr Neil de Wet said the viral illness spread easily and more cases may yet be discovered. APNZ