The Canterbury District Health Board is urging people to immunise their children against measles following an outbreak of the disease.
The DHB has confirmed three cases in Christchurch. Another 15 cases have been confirmed in Auckland and two in Wellington.
Canterbury Medical Officer of Health Ramon Pink says of the three Canterbury cases, two people were not immunised and the third had had only one of the two shots needed to ensure immunity.
Dr Pink says measles is serious, and one in 10 people who contract the disease will require hospitalisation.
The only defence is immunisation and if parents have not immunised their children they should see their doctor, he says.