A warning has gone out to the public about the collection or consumption of shellfish from all of Akaroa Harbour near Christchurch.
The Canterbury District Health Board has issued the warning after a number of routine tests revealed levels of Diarrhetic Shellfish Poisoning (DSP).
Those tests found toxin levels in the tested shellfish showed traces of DSP up to 0.76mg/kg.
The Ministry of Primary Industries recommended safe level is only 0.16mg/kg.
"Mussels, oysters, tuatua, pipi, toheroa, cockles, scallops, cats-eyes, kina (sea urchin) and all other bivalve shellfish should not be eaten," CDHB Medical officer Ramon Pink says.
"Symptoms of diarrhetic shellfish poisoning typically appear within half an hour and can last for 24 hours.
"If anyone becomes ill after eating shellfish from an area where a public health warning has been issued, phone your usual general practice team and they can advise what to do."
Newshub has approached the CDHB to determine why the shellfish have suddenly become poisonous and unsafe to eat, but monitoring of toxin levels will continue until levels drop to a safe level.