Thousands of people could have been exposed to measles at a kapa haka festival over the weekend.

Waikato District Health Board announced this afternoon that it had been notified of five cases of measles in the region.

In the most recent case, the infected person was still contagious when they visited the regional Tainui Waka Kapa Haka festival on Saturday.

About 5000 people from throughout the North Island attended the event at the Claudelands Event Centre in Hamilton.

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Seventeen Tainui Waka Kapa Haka groups - from Coromandel down to South Waikato including Waikato, Hauraki, Maniapoto and Raukawa - competed at the event.

In another case, the infected person attended Nga Taiatea Wharekura School while contagious.

Two of the five measles cases have required hospitalisation.

The first symptoms of measles are fever, runny nose, sore runny eyes and cough. The rash starts later.

"If you or your child attended this kapa haka event you may have been exposed to the measles virus," the DHB said.

"You should look out for the symptoms of measles for 14 days after the event."

Waikato DHB medical officer of health Dr Felicity Dumble said it was a timely reminder to everyone to check that they and their children are fully immunised against measles.

Vaccination gives people full immunity in the vast majority of cases.

People without immunisation should get inoculated with the MMR vaccine as soon as possible, the DHB said.

• If you or your child becomes unwell please phone your GP or call Healthline on 0800 611 116 for advice.