Health officials have been sent to a youth camp on Motutapu Island in the Hauraki Gulf, after a young man attending the camp died of meningococcal disease.
There are 190 people attending the camp for St John Youth but only a few are considered to be at risk of infection.
Auckland Regional Public Health Service is sending staff to provide support to people at the camp.
Northland's Public Health Unit is talking to the man's family about who else he may have been in contact with in the past week.
Medical Officer of Health Denise Barnfeather said the sometimes fatal disease could be difficult to diagnose.
Symptoms include fever, headache, vomiting, feeling confused or delirious, joint pains, aching muscles, stiff neck, and purple or red spots or bruises.