Public health officials are warning passengers on an incoming flight from Singapore this week may have been exposed to measles.

A six-year-old boy on Air New Zealand flight NZ281, which arrived at Auckland International Airport from Singapore at midnight on Wednesday, was infectious.

The passengers closest to the boy were seated in rows 34 to 49.

Any passengers on the flight who start to feel unwell should phone their doctor or call Healthline on 0800 611-116 for advice.

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"It could be another five days before symptoms appear in other passengers but if anyone seated in those rows knows they don't have immunity to measles they can be vaccinated, and that could prevent the symptoms developing," Auckland Regional Public Health Service medical officer of health Dr David Sinclair said.

"If you feel unwell, please don't visit your doctor. It is important to call first, because measles is highly infectious and people with measles can infect others in the waiting room."

The health service is attempting to contact all people were exposed to see whether they are susceptible to measles infection, and offer advice including further immunisation, or possibly isolation to avoid spreading the disease.

One in 10 people with measles need hospital treatment and the most serious cases can result in deafness or swelling of the brain.

It is one of the most infectious airborne diseases.

"It is very easily transmitted from one person to another, possibly just from walking past the passenger with measles, or while sitting near them in the airport gate lounge," Dr Sinclair said.

"People tend to underestimate measles," Dr Sinclair said.

"The reality is it can be a nasty disease."

People most at risk are those who have not had the measles, mumps, rubella (MMR) vaccine, or who have just had one dose of the vaccine. Anyone born before 1969 is likely to be immune to the disease without having had the vaccine.

"The only way to protect from measles and the best way to avoid its complications is to be fully vaccinated," Dr Sinclair said.

"My plea would be for parents and families to check that their children's immunisations are up-to-date."

It can take up to 21 days to develop symptoms.

There were big measles outbreaks in 2011 and 2014, both of which started by people who were infected overseas.

Measles symptoms:

- The first symptoms are a fever, and one or more of a runny nose, cough and sore red eyes
- Then after a few days a red blotchy rash comes on and lasts up to one week. The rash usually starts on the face and spreads to the rest of the body
- Children and adults with measles are often very sick.

How to protect you and your family against measles:

- Make sure your children and family are fully immunised with two doses of the vaccine. Immunisation is the best protection against many diseases and complications.
- Measles can't be treated once you get it. The only way to prevent the disease is through immunisation.
- Call Healthline 0800 611 116 for Free Health Advice