People in the upper North Island are being warned not to collect shellfish, after a spate of paralytic shellfish poisoning.
Thirteen people have been hospitalised already this month, including two who ended up in intensive care.
Medical health officers are warning of high toxic algae levels and advising not to eat shellfish from as far south as the Taranaki coastline and Bay of Plenty - to Kaipara Harbour and Dargaville in the north.
Clinical director for public health in the Auckland region Dr Julia Peters says there's a high likelihood people will get sick if they collect and eat the shellfish - even if they cook them first.
She says the effects of the toxins can be extremely serious, and there is no treatment.
Dr Peters says hospitals can only support people to stay alive until their system becomes free of the toxin.