Simon Nellist was training for a charity ocean swim when he was attacked from below by the creature at Buchan Point, Malabar about 16km (10 miles) south of the city.

Mr Nellist's body suffered "catastrophic injuries", officials said.

He was reportedly an experienced ocean swimmer and friends said he "loved the water".

It is believed Mr Nellist was a British expatriate living in the Wolli Creek area of Sydney and was engaged to be married.

The Malabar Magic Ocean Swim has since been cancelled "out of respect" for Mr Nellist.

In a statement, the organising committee said: "The organising committee extends our thoughts and prayers to the family of the swimmer who was so tragically taken yesterday.

"Out of respect for the swimmer and his family, and following wide consultation with Randwick Council and experienced senior Surf Life Saving personnel, we believe that cancelling the 2022 swim is appropriate."

Wednesday's incident was the first fatal shark attack in Australia's largest city since 1963.

New South Wales Police said in a statement: "Detectives from the Marine Area Command are appealing for information as they continue to investigate a fatal shark attack at Little Bay yesterday.

"About 4.35pm on the 16 February 2022, emergency services were called to the Little Bay northern headland after reports a swimmer had been attacked by a shark.

"Officers attached to Eastern Beaches Police Area Command with assistance from the MAC and Surf Life Saving NSW attended and located human remains in the water.

"Police are encouraging anyone who may have seen the man before or during the incident to contact Crime Stoppers on 1800 333000. Information is treated in strict confidence."

Several of Sydney's beaches, including the iconic Bondi and Bronte, were temporarily closed as officials hunt for the killer shark.

The beaches have been cleared to reopen on Friday, 18 February.

Drum lines, which are used to bait sharks, have been set up near the attack site off Little Bay beach, while drones have been deployed to see if the shark is still in the area.

"This has been a complete shock for our community," said Dylan Parker, the mayor of Randwick Council which includes Little Bay.

"Our coastline is our backyard and to have a tragic death under such horrifying circumstances is completely shocking."

A spokesperson for the New South Wales Department of Primary Industries said its shark biologists believe a white shark at least three metres (9.8 feet) in length was likely responsible for the attack.

Authorities have ordered people to stay out of the sea as temperatures hovered around 30C (86F).

"A few crazy surfers still go out and take the risk but most of us take notice and just stay out of the water until the sharks have gone. It's a lot more dangerous driving, to be quite honest," local resident Karen Romalis told Reuters news agency.

An FCDO spokesperson said: "Our consular staff are in touch with the New South Wales Police regarding a shark attack in Sydney. We are supporting the family of a British man and our thoughts are with them at this difficult time."