People are being warned to steer clear of shellfish from parts of the North Island or risk getting sick.
High levels of paralytic shellfish poison have been found from Taranaki to Dargaville and in the Bay of Plenty.
The toxin contaminates the gut of shellfish and is not removed by cooking.
The warning covers the popular Manukau and Kaipara harbours.
Simon Baker, the Auckland Regional Medical Officer of Health, says if eaten, the toxin can cause paralysis and breathing problems.
Dr Baker says it is not known when it will be safe to collect shellfish again.