Rotorua's firefighters are on alert after a a participant in last weekend's charity Sky Tower climb was confirmed as having measles.
Public health officers have been racing to trace the hundreds of people who may have been exposed.
A person who stayed at SkyCity hotel at the weekend and took part in the Firefighter Sky Tower Stair Challenge developed measles symptoms after returning home to Palmerston North.
Volunteer firefighters from Lake Okareka, Ngongotaha and Mamaku also took part in the challenge.
Chief Medical Officer Don Mackie said a large number of people from many parts of the country were potentially exposed, and public health units nationwide had been notified.
"If you are someone who thinks you might have been at risk of exposure, it's important you contact your local public health unit," Dr Mackie said.
"Public health officials are well versed in carrying out what is known as contact tracing, which involves reaching as many people as possible who could have been potentially exposed to measles. They can then be advised about what measures they need to take if they have, or develop measles-like symptoms."
It usually takes 10 to 14 days for someone who has caught measles to show symptoms. Those who are not immunised and may have been infected will be advised to stay at home for 14 days.
Measles is highly contagious, and can be caught without direct contact as the virus can stay in the air for up to an hour.
Dr Mackie said the case showed how important it was to be immunised, and people who were unsure should check their immunisation status.
Lake Okareka Chief Fire Officer Phil Muldoon said he had notified all members of the team.
"We'll be keeping an eye out for any symptoms," he said.
-People who think they might have been exposed should phone their GP or Healthline on 0800 611 116 or advice.
It's important not to visit a doctor without calling first so measures can be taken to avoid infecting others.