Over 100 people may have been exposed to measles as an outbreak continues to spread across the South Island.
Five cases have already been confirmed, with infected patients visiting supermarkets, restaurants, campgrounds and other public places.
- Two new measles cases as disease spreads in South Island
- Queenstown measles victims weren't immunised
- Three measles cases after exposure at Queenstown Airport
Canterbury Medical Officer of Health Dr Ramon Pink is hunting for patient zero, trying to work out who brought the disease in.
"Because we don't know where the source of measles is, who the individual was that was infectious, we don't know where they may have travelled," he said.
The highly contagious virus first showed up at Queenstown Airport late last month.
It's now spreading across the South Island, with separate cases confirmed in Wanaka, Queenstown, Christchurch and Nelson.
"Measles starts off as non-specific symptoms; a cough, runny nose, and a temperature over three or four days - and then a rash," Dr Pink said.
Measles was officially eliminated in New Zealand just six months ago, thanks to vaccines. It's thought the infected person may have come in from Australia - where there's been an outbreak recently.
Otago University public health expert Professor Michael Baker says it's a wake-up call.
"We can never be complacent about this disease, we need really high immunisation coverage if we want to protect our population and also contribute to the global effort to eliminate measles," he said.
It's now to a race to stop it spreading even further, public health officials trying to alert over 100 people across the South Island who may have been exposed.
"The key is making sure people are vaccinated, it is available, and they can access that," Dr Pink said.
If you're worried you may have contracted measles, the message is to call your doctor.