It's believed a Northlander confirmed with measles was infected at a national Kapa Haka event held in Waikato last month.
The Kaeo resident attended the national Kapa Haka event at Claudelands Events Centre on April 16.
At least 11 other measles cases have been confirmed in Waikato following the event.
Medical Officer for the Northland DHB Dr Virginia McLaughlin says this demonstrates how easily spread the measles virus is.
"Measles is highly infectious and if children are not immunised there is a very high chance they will get sick if exposed to someone with measles."
Dr McLaughlin is urging all Northlanders to make sure their families are immunised, as the best protection from the potentially serious disease.
"Measles is spread by tiny droplets in the air and is very infectious, easily spreading to those nearby.
"Measles can be a very serious illness, [but] is an avoidable disease where there is an effective vaccine."
Dr McLaughlin says immunisation protects not only individuals but also stops the spread within communities.
Initially, measles symptoms include fever, coughing, a runny nose and red eyes and are often mistaken for a cold.
A rash generally appears on the face and neck and spreads over the body three to five days later.
Anyone displaying the symptoms of measles should immediately telephone their doctor or Healthline on 0800 611 116 for advice.