Poor levels of immunisation and high volumes of international travel are causing measles to spread but the risk of a widespread epidemic is low, Auckland's Medical Officer of Health says.
Eighty-nine people have been affected by measles nationwide since last December, mostly in Auckland.
Auckland Medical Officer of Health Richard Hoskins said the sheer number of cases and sporadic infections meant people infected with the disease were difficult to quarantine.
However, it was unlikely thousands of people be affected, he said.
"What we're much more likely to see is a big, sustained outbreak, which is really just contained in one region.
"So not widespread throughout New Zealand but much more likely to see the numbers going into the hundreds."
Measles could cause permanent damage, such as hearing loss, in some people so isolating infectious people was important to stop the disease spreading, Dr Hoskins said.