Beachgoers have been warned to be extremely cautious on Coromandel's west coast after the death of a dog from the same toxin which has killed five dogs on Auckland beaches.
Warning signs went up on the peninsula on Thursday after a dog which had been at Tapu Beach tested positive for tetrodotoxin.
The toxin has been found in seaslugs and in 15 dogs which became unwell in Auckland's Hauraki Gulf beaches.
Thames Coromandel District Council environmental services manager Craig Birkett says children and pets should be supervised and no sealife should be touched.
The council is watching the area and asking for sightings of seaslugs, he says.
Waikato District Health Board warns even a small dose of the toxin could be fatal.