SYDNEY (AFP) - A man was killed by a shark in front of his wife on Tuesday at a popular Australian beach after being bitten on the leg while swimming, officials said.

The man, in his 50s, was in the water at Byron Bay on the New South Wales north coast, a popular tourist destination, when he was spotted floating with a wound to his leg.

"Other swimmers pulled him onto the beach with a very serious bite to his leg," a New South Wales ambulance spokesman told AFP. "It is suspected to be from a shark."

A doctor was on a beach in the area at the time and tried to save the man but he was pronounced dead at the scene.

"He was only 15 or 20m from the beach," Inspector Bobbie Cullen told reporters.

"Obviously, the witnesses are extremely distressed and we will be taking formal statements off them and (what happened) will become a lot clearer," she added.

Police said his wife was watching from the beach when the attack occurred.

A large shark believed to be a great white was spotted near the area soon after the attack.

Beaches in the area were closed while authorities tracked the animal and tried to force it out to sea using helicopters and jet skis.

Mr Mark Hickey, 52, was one of the first on the scene and told News Limited newspapers that he saw a "6 or 7 foot" shark.

"I saw what looked like seaweed but it was blood in the water," he said.

"The shark came back to him and had another go. I didn't know it was a person - but when I realised I ran out and waded to the bank and grabbed him and did CPR but it was too late."

Experts say attacks by sharks, which are common in Australian waters, are increasing as water sports become more popular.

Before Tuesday's incident, the last fatal shark was in April at Tathra Beach about 350km south of Sydney.

Only the swimming cap and goggles of the woman who was taken were recovered.