A large blue-ringed octopus spotted in the shallows of a popular beach on WA's mid-west coast has sparked alarm during the peak summer season.

How to treat a blue-ringed octopus bite 1. Perform DRSABCD 2. Calm the patient and keep them still 3. Apply a crepe bandage over bite site 4. Firmly apply a heavy crepe pressure bandage, starting at the fingers/toes and working up as far as possible 5. Immobilise the bandaged limb using splints 6. Ensure an ambulance has been called Source: St John Ambulance

Michelle-Ann Treasure photographed the highly-venomous cephalopod while at Medallia Beach in Geraldton with her family and shared the images on Facebook to warn others to take care.

Hundreds have since shared the pictures and expressed concern over visiting the area.

Curator of molluscs with the WA Museum, Lisa Kirkendale, said while blue-ringed octopus are widespread, it was rare to spot one.

"We have records from along the coast from Albany through Esperance, up through Geraldton, up the top end in the Kimberley as well as the east coast and all along the south," she said.

"It's actually very special to see one. Just respect that the ocean is their home and it's expected and natural for them to be in coastal areas."

This specimen measured about 20 centimetres, which is considered large as many are just 5 centimetres.

Dr Kirkendale said blue-ringed octopus are identifiable by the blue circles or stripes on their body.

"They kind of flash iridescent when the animal is on the move or disturbed," she said.

No anti-venom exists

Dr Kirkendale said bites are rare, but people are advised not to touch the blue rings or try to pick them up as the octopus is more likely to bite if they are lifted or handled roughly.

"They're delicate and fragile creatures," she said.

The WA Museum has a number of blue-ringed octopus specimens and photographs recorded along the WA coast. ( Supplied: WA Museum )

"If you're bitten you might not actually feel much so if you think you've been bitten it's important to seek medical attention right away.

"You can apply pressure right away and do artificial respiration.

"There are two known toxins, but no anti-venom exists and it's important to be careful. But people have survived the bites of these animals."

Dr Kirkendale also warned against picking-up shells.

"They do like to inhabit small shells or even pieces of garbage, so do not carry objects such as empty shells or beach trash in your wetsuit or in your pocket," she said.

Those doing coastal clean-ups should wear protective gloves and people bringing in mussel, cray or crab pots should check them carefully.

The president of the Champion Bay Surf Lifesaving Club, Peter Nelson, said he had never seen one at the beach, but they had been spotted in reefs further offshore.