Swimmers and dog owners have been warned off entering the water near Kurnell Peninsular, south of Sydney, after a dog was eaten by a shark.

The dog was swimming in shallow waters off shore when a shark attacked the dog at Bonna Point, near the headland of Botany Bay on Sunday.

The shark - believed to be a bull shark - has sparked authorities into action with lifeguards warning people to avoid the water.

The Sutherland Shire Council released a statement telling beachgoers to stay away from the water when it is dark or during twilight.

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"Council lifeguards are at the Kurnell beaches advising swimmers and pet owners to keep out of the water and they have installed signs to alert the public to the shark sighting," the statement read.

"NSW Department of Primary Industries advises people to avoid swimming or surfing when it is dark or during twilight hours and encourages the use of the SharkSmart app which has safety tips for swimmers, surfers, divers, snorkelers and spearfishers."

The attack comes only a few weeks after a two metre bull shark was caught on camera only metres off shore at La Perouse in Sydney's south.

Only days before spearfisherman spotted another shark at Port Botany.