Three cases of measles have been confirmed in the South Island after people were likely exposed to an infected person at Queenstown Airport.
In the last four days, cases of the highly infectious viral disease have been reported in Queenstown, Wanaka and Christchurch.
The exposure happened on March 21 or 22. None of the three people who contracted measles had been immunised.
Canterbury District Health Board (DHB) says the person who infected them may only have been mildly ill, and will be fully recovered by now.
People are most likely to become ill between April 10 and 20 if they have contracted measles from one of the three infected people.
Canterbury DHB Medical Officer of Health Dr Ramon Pink says those experiencing the symptoms of measles shouldn't go to their GP or an after-hours clinic to avoid spreading the illness, and should call a medical professional for advice.
"People are infectious from five days before the onset of the rash to five days after the rash starts and should stay in isolation during this time," says Dr Pink.
"This means staying home from school or work and having no contact with unimmunised people."
Those who have not received two MMR vaccinations are at a greater risk of infection. The vaccine is freely available from all practices.
The Canterbury DHB says anyone else who was exposed to measles at Queenstown Airport are now at the end of their maximum incubation period and are unlikely to become ill at this point.
It is investigating the cases with the Southern DHB, and identifying and contacting those who may have come into contact with any of the three confirmed cases.
The most common initial symptoms of measles are a dry cough, runny nose and high temperature. After four or five days a rash will usually develop, spreading from the face to the chest and arms.
People with symptoms can call Heathline on 0800 611 116.