People visiting Auckland's eastern beaches are being warned not to touch dead marine life or birds, following the identification of the deadly toxin blamed for the death of at least one dog.
A toxin more commonly found in puffer fish, tetrodotoxin, has been discovered in sea slugs on several beaches, which were eaten by dogs.
Hospital emergency departments in the Auckland region have been briefed by public health officials on the toxin.
The Auckland Regional Public Health Service has reiterated its warnings that children and animals should not visit Hauraki Gulf beaches. Adults who visit eastern beaches should avoid touching dead marine life or birds, collecting shellfish or going swimming.
Medical Officer of Health Dr Denise Barnfather says the poison can cause violent reactions in humans and there is no no known antidote.
People who ingest it could experience tingling, numbness and sweating, along with seizures and possible paralysis.
Toxin not seen in NZ before
Scientists at the Cawthron Institute in Nelson say this is the first time the toxin has been found in this country. Researcher Paul McNabb says it's not clear how it has been getting into sea slugs.
"Sea slugs are consuming something which contains tetrodotoxin and that's killing them. They're washing up on the beach, and dogs are dying from consumption of those sea slugs.
"The mystery is where the tetrodotoxin is coming from in the environment and that's what we're still working on."
The toxin first attacks the nervous system and can kill animals that ingest it within an hour. It can also kill humans within 60 minutes, but people are put off by a putrid odour.