People are being warned not to collect or eat shellfish from Raglan Harbour and the Waikato's west coast this weekend.
The Ministry for Primary Industries has detected concerning levels of paralytic shellfish poisoning toxins in the area, which could make shellfish dangerous to eat.
A public health warning has been issued for the coast between the Waikato River mouth and Papanui Point just south of Raglan.
MPI says mussels, oysters, tuatua, pipi, toheroa, cockles, scallops, catseyes, kina and all other bivalve shellfish shouldn't be eaten, and cooking won't remove the toxin.
Paua, crab and crayfish may still be eaten if the gut has been completely removed prior to cooking.
Anyone who eats the shellfish is being asked to seek immediate medical attention, and keep leftover shellfish for testing.People are also being advised to call Healthline for advice on 0800 61 11 16, and advise their nearest public health unit.