Toxic sea slugs have been found by scuba divers in Whangarei Harbour.

Northland DHB has issued a warning for beachgoers after tests confirming the two slugs contain potent neurotoxin tetrodotoxin.

The toxin is normally found in poisonous species including the puffer fish and blue ringed octupus.

Medical Officer of Health Dr Jonathan Jarman says people need to use common sense to make sure their children and pets don't come into contact with the slugs.

"We are advising people not to touch or eat dead things on the beach and always supervise children around water. This advice is really just common sense. If a person becomes unwell after eating a dead thing on the beach, they should seek medical attention," he says.

Toxic sea slugs were blamed for the death of dogs on Auckland beaches in August last year.

Early symptoms of tetrodotoxin poisoning include numbness and tingling around the mouth, and nausea.

Numbness and tingling can spread to the face, tongue and other areas, followed by paralysis, uncoordination and slurred speech.

No human poisoning cases have yet been reported in New Zealand.

Northland DHB advice:

• Don't touch or eat dead things on the beach. Always assume anything dead on the beach is potentially poisonous.

• Always supervise children around water.

• Seek medical attention if people become unwell after visiting the beach particularly if they had contact with dead things on the beach.

- NZ Herald staff