A vaccinologist says the number of Kiwi patients being treated for measles has reached approximately 65.
Helen Petousis-Harris told The AM Show on Wednesday the disease was one of the "most infectious known to man".
"If I was infectious and came to visit you today and any of you were susceptible in this room, you would probably get measles. The people coming for several hours afterwards would probably get measles too, if they're susceptible."
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She said people with the disease usually don't show symptoms for around two weeks, in that time they are most likely to spread the disease on to others.
Measles can contribute to other health problems including brain damage and pneumonia, the most likely cause of death for youngsters who catch the virus.
Ms Petousis-Harris said the current Canterbury outbreak could have come from the Philippines, where cases are high.
"Previous outbreaks have been traced to the Philippines, so it's a likely source.
Three years ago we were declared measles free, which means there were no cases sustained in New Zealand, they had to be imported."
She said there was huge concern over the movement of anti-vaxxers, who were contributing to the spread of the possibly deadly disease.
"Anyone who doesn't take the vaccine puts themselves and their child at risk of what is potentially a serious disease.
"Do you want to get your health information from the wife of a football player who spent a few hours on social media and Google or do you want to consult the last 200 years of scientific investigation and knowledge and the advice of entities like the World Health Organisation and your own GP?"
She said herd immunity works, but only if people join in.
"We have holes in our herd and measles are very good at finding those holes."