Seven cases of measles have been confirmed at a tertiary institution in Palmerston North.
MidCentral District Health Board said it was working with the Institute of the Pacific United to trace where the outbreak started.
The institute cancelled classes for two weeks as a result of the outbreak and is warning that could be extended.
The students in halls of residents who have measles are in isolation and food is being delivered to them.
Certain parts of the institute are closed, including the dining hall and library, and students and staff are being told to stay away.
"Measles spreads from person to person through the air from breathing, coughing and sneezing, and contact with those secretions," said Medical Officer of Health, Dr Greg Simmons.
"The disease is contagious from just before symptoms begin until about five days after onset of the rash. The illness usually starts between 10 and 14 days after contact with the measles virus."
The district health board said measles is a very infectious disease for those who are not immunised, and urged people who think they might have it to stay home.
Symptoms include a fever, runny nose, cough, and sore, red eyes.
The institute asked all students and staff to provide proof they had been immunised.
Those who had not been immunised would be able to receive vaccinations on campus this week, it said.