A second case of measles signals the disease has gained a foothold in Christchurch, health officials say.
A new case has been diagnosed in the city, with no known connection to the 4-year-old diagnosed with measles earlier this month.
Canterbury Medical Officer of Health Dr Cheryl Brunton said the second case indicates measles has a foothold in the community.
"This is a very contagious disease and it's quite likely we will get more cases. The good news is immunisation is a proven way to stop the spread," she said.
Dr Brunton said the source of the new case was being investigated, but there was no known connection between the two.
In both cases, the child had received their first vaccination dose at 15 months, but not the second, which is given at age 4.
The 4-year-old who was earlier diagnosed has passed the infectious stage and has returned to preschool.
Advice had been given to the two preschools involved and to parents.
"The advice urges parents who have not immunised their children to do so," Dr Brunton said.
"While we are continuing to trace the source of the disease, the key to preventing the spread is in the hands of the community."
Measles starts with a fever, runny nose, cough, red eyes and a sore throat. It's followed by a rash that spreads over the body.
It's highly contagious and spreads through the air through coughing or sneezing.
If you believe you or someone in your family has measles, phone your doctor before visiting a clinic.