AKIPRESS.COM - A man has been killed by a shark at Byron Bay in northern New South Wales, ABC News said.

The man, 50, was pulled from the water about 10:45am (AEST) after he was seen floating close to the shore, NSW Police said.

He had suffered a significant injury to his right leg.

NSW Police said the man was from Byron Bay and has been formally identified by a family member.

It is believed the man had been alone off Clarkes Beach when he was attacked.

Onlookers performed CPR until police arrived, but resuscitation stopped soon afterwards.

A spokesman for the ambulance service said it was likely the man went into cardiac arrest when he was in the water.

It is believed his family have arrived at the beach. One of those at the scene was visibly distressed.

Helicopters and jetskis have been patrolling the the area and a short time ago a large shark, believed to be a great white, was spotted close to the shore.

Authorities were hoping to herd it further out to sea.

The town's main beach will be closed until at least Wednesday afternoon.