Three cases of measles have been confirmed in Rangiora and Christchurch in the past four days.
A teenage boy, and a man and woman in their 40s are sick.
None are thought to be have been fully immunised against measles.
Unimmunised people who come within two metres of an infectious person have a 90 percent chance of contracting the disease.
Canterbury DHB Medical Officer of Health Dr Ramon Pink says they are awaiting test results for a small number of suspected cases.
Take your Radio, Podcasts and Music with you