Public health workers fear they may not be able to contain the measles outbreak that started with the arrival of an Emirates flight from Brisbane on January 11 and is spreading in the community.
At least 300 people who have come into contact with the highly infectious disease during the outbreak have been traced by public health workers.
Eleven cases have been identified: 10 in Auckland and one in Wellington. The sufferers are aged between 5 months and 19 years and two have needed hospital care.
But of greater concern is that while nine of these people were on Emirates flight EK 434 from Brisbane, two were not, indicating measles is spreading from person to person in Auckland.
"The only connection is that they live in the same part of Auckland as some people from the flight," said medical officer of health Simon Baker.
He would not name the area.
"They could have been in the dairy before them; they could have coughed on them in the mall. Measles is very catchable, so it doesn't take much.
"People are infectious before they have got measles. You can't really blame people for spreading it if they didn't know they had it.
"We've got nurses who are speaking to all the cases and the cases' families, finding out where they have been in the infectious period and trying to find as many people as we can who have been in the same places. [They are] ringing them and giving them health advice ... That's at least 300 people," Dr Baker said.
Cases have been isolated at home until they are considered no longer infectious - five days after the start of the measles rash, which typically lasts for about seven days.
Dr Baker said it was impossible to know if the outbreak would spread. There were the two unrelated cases and "the concern is that we may not be able to contain it. We are hoping that we can".
The first passengers on the Emirates flight to be diagnosed were part of a group that had travelled to the Philippines and Singapore. They would have been infectious during the flight.
* Highly infectious.
* Incubation period around 10 days.
* Patients infectious for one day before symptoms, and for five after rash starts.
* Causes coughing, sneezing, fever, sore red eyes, white spots in mouth.
* Typically one death, one brain inflammation and 100 hospital admissions for every 1000 cases.
* Authorities say to check with your GP that your family are immunised.
* If measles is suspected, phone your GP, or Healthline on 0800 611 116.