The Waikato District Health Board has declared a measles outbreak and is urging people in the region to get immunised.

The District Health Board has been notified of six cases of measles in the last week, with two of those cases going back to late December.

The DHB's chief medical officer of health, Dr Richard Hoskins says the DHB had been working with the families to find out where they might have contracted measles from.

Measles can lead to complications such as pneumonia, seizures, and swelling of the brain, with about 20 per cent of measles cases resulting in hospitalisation.

"Measles is easily passed from one person to another. The best form of protection is immunisation."

"Anybody whose not had measles in the past and not been vaccinated is probably susceptible to measles and is very likely to get it if they spend time indoors with somebody with measles."

The first symptoms of measles are a fever, runny nose, cough or red eyes, followed by a red, blotchy rash a few days later, which usually starts on the face and spreads to the rest of the body.

Anyone who suspects they have measles should call their GP or Healthline, but they must call ahead so they can be examined in isolation and not infect others in waiting rooms, says Dr Hoskins.

People who are infectious - which is four days before the rash comes out, to five days after - are being told to stay in isolation, and not go near public places.

If someone isn't sure if they have been immunised, they can contact their GP, check the immunisation register - if they were born after 2004, look at their Plunket Book or get a blood test.

Immunisation is free, including the doctor's appointment.