Wellington High School has sent an urgent message to parents saying one person has been diagnosed with the disease.
The warning relates to staff or students who were in five specific classes last Monday - including biology, chemistry and psychology. Those people should only go to school if they can confirm they have been vaccinated or have already had measles.
There have been 24 confirmed cases of measles in Wellington so far this year.
Medical Officer of Health Dr Annette Nesdale told Morning Report officials were keeping on top of the spread of the virus in Wellington.
"Each time we get a measles case we look to see 'has it come from a local spread in Wellington or has it come from overseas or Auckland'.
"In this case it's clearly come from Auckland.
"We don't have community spread in Wellington and we want to keep it that way for as long as possible."
Dr Nesdale said immunity rates in Wellington were good, but not optimal.
"We have good levels of immunisation, but you need excellent levels ... you need, really, 95 percent of the whole community protected to stop spread.
"With isolated cases we can get on top of the spread."
She said parents who were unsure whether their children were immunised should contact their medical centre.