There's a possible case of measles at Kelston Boys' High School in west Auckland

The Auckland Regional Public Health Service is advising anyone who visited the school between September 20 and September 25 to watch for symptoms.

Measles usually begins with a high fever, runny nose, cough and sore red eyes, followed by a rash starting behind the ears and spreading to the body a few days later.

Medical Officer of Health Dr Rob Parker says one in three people with measles will develop complications, such as ear infections, pneumonia, diarrhoea - and in rare cases inflammation of the brain.

He says people who have visited the school during this time and are feeling unwell should immediately telephone their doctor or Healthline for advice.