The public is being warned not to eat shellfish from a large area of Bay of Plenty coastline after a dozen people became sick with paralytic shellfish poisoning.
The warning affects a long stretch of coast from Whangamata on the Coromandel Peninsula, to the Whakatane river mouth.
The Bay of Plenty's medical officer of health Phil Shoemack said paralytic shellfish poisoning was caused by natural toxins, produced by algal blooms.
He said it could make some people very sick.
"This problem of paralytic shellfish poisoning can range from just a mild bit of tingling and numbness in your fingers or around your lips and mouth, to quite significant symptoms, a couple of years ago when we had a similar problem we had a couple of patients admitted to intensive care and needing to be put on a ventilator to help them breathe."
Dr Shoemack said because it was a chemical toxin, freezing or cooking shellfish would not remove it.