Public health authorities say there is an outbreak of legionnaires' disease in Auckland.
The health service says nine people from throughout the region have contracted the disease - a form of pneumonia - in the past six weeks.
It says typically in that period it would only see about two cases.
Auckland's Medical Officer of Health Simon Baker says it is possible the cases are linked, but there could be more than one source.
Dr Baker says the disease is contracted through water vapour from cooling towers and is urging building owners to use biocide to kill any legionella bacteria that could be present.
In 2011, two people died from the disease out of 50 cases, he says.