A stretch of Northland's east coast is out of bounds for gathering or eating shellfish due to dangerous levels of toxins found in samples.

The Ministry for Primary Industries (MPI) has issued a public health warning about collecting or consuming shellfish from the between Cape Brett in the north to Taiharuru Head in the south.

Routine tests on shellfish samples taken from this region have shown levels of paralytic shellfish poisoning (PSP) toxins of up to 1.5 mg/kg, well above the safe limit of 0.8 mg/kg set by MPI.

Anyone eating mussels, oysters, tuatua, pipi, toheroa, cockles, scallops, catseyes, kina and all other bivalve shellfish from this area could potentially become ill.

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Cooking shellfish does not remove the toxin. Paua, crab and crayfish can be eaten if the gut has been completely removed before cooking, as toxins accumulate in the gut.

In November the Far North east coast between Rarawa Beach and Cape Karikari, including Houhora and Rangaunu harbours, was affected by PSP toxins.

Symptoms appear between 10 minutes and 3 hours after eating contaminated shellfish, and may include numbness or tingling around the mouth, face, and extremities, difficulty swallowing or breathing, dizziness, headache, vomiting, diarrhoea, paralysis and respiratory failure.

Serious cases were rare in New Zealand but people around the world die from PSP every year.

Anyone who becomes ill after eating shellfish should phone Healthline on 0800 61 11 16, or seek medical attention immediately. They should also contact the nearest public health unit and keep any leftover shellfish in case it can be tested.

Commercially harvested shellfish - sold in shops and supermarkets, or exported - will be subject to strict water and flesh monitoring programmes by MPI.

MPI takes shellfish and seawater samples every week from popular shellfish gathering areas around New Zealand.