Mosman Council said multiple bites had been reported at Balmoral Beach over the last week.

The blue-ringed octopus is one of the most venomous animals in the world.

If bitten, the venom can cause paralysis and stop breathing.

Anyone bitten is advised to seek medical assistance immediately.

“Council was notified by Royal North Shore Hospital that several cases had occurred, to allow Council to provide information to the community to raise awareness about taking care in these areas,” a spokesperson for Mosman Council said.

The local health district could not confirm any specific incidents and bites do occur in the area from time to time.

Blue-ringed octopuses live in tidal pools and reefs around Australia.

The blue colour only becomes easily visible when they are threatened, so by the time a person recognises the creature as a blue-ringed octopus, it may be too late.

Most of the time, they just look like regular brown octopuses.

They grow to a maximum size of 20 centimetres outstretched and weigh about 100 grams.

Symptoms from a blue-ringed octopus bite include a painless mark with a spot of blood visible; numbness around the mouth, lips and tongue; muscle weakness, and difficulty breathing.