Macleans College is "taking the stance" any of its 2500 students could be infected with measles after a pupil was confirmed as having the virus.
Parents and caregivers of students who haven't been immunised have also been told via email to keep them home in quarantine until Friday, August 16.
Macleans College principal Steven Hargreaves said the school, after a call from the regional public health service, yesterday decided to take a cautious approach to the situation.
"I've emailed the whole parent community to say if your student is not immunised then they should stay off school", he said.
"The [infected] student attended a school assembly, they spent time in the common space for their house, they travelled to and from on the bus for two days, and therefore we couldn't narrow down the group of students he might have been in close contact with.
"Fortunately for us, the student was away all last week, so that hopefully has narrowed down the number of students that have been exposed."
Symptoms of measles, a serious viral infection which spreads quickly, include a high fever, runny nose, cough and sore red eyes.
A few days later a rash appears on the face and neck before spreading to the rest of the body. About one in 10 people with measles need hospital treatment.
A concerned parent contacted the Weekend Herald after emailing the school to see which groups of the school were most at risk.
She was told the school was "taking the stance that any student may have been exposed".
The mother said her child, who was in Year 10, was immunised after receiving both of their MMR vaccinations but was concerned for other students.
Meanwhile, the total number of measles in Auckland as of 12pm yesterday totalled 369 confirmed cases, the Auckland Regional Public Health Service said.
Of those, 156 people had been hospitalised; resulting in a 43.8 per cent of cases ending up at an emergency department.
The Counties Manukau District Health Board recorded 216 people had been hospitalised, Auckland DHB said they had seen 47 cases and the Waitematā DHB 93 cases.
Health Navigator NZ reports measles is easily spread from an infected person by saliva or mucous droplets when coughing, sneezing or talking.
"Just being in the same room as someone with measles can lead to infection if you are not immunised."
Key points about measles:
• One person with measles can pass on the disease to 13 other people who have not been immunised.
• A person with measles is infectious from 5 days before and until 5 days after the rash appears, about 10 days in total. During this time the infected person needs to stay away from other people. Children need to be kept home from school and adults from work. Do not invite other children or visitors to your house.
• Measles during pregnancy increases the risk of miscarriage, early labour and low birth-weight babies.
• Vaccination with the MMR vaccine is the best way to protect against measles. You need two doses to be fully immunised.
Source: Health Navigator NZ