A man believed aged in his 50s is dead after being mauled by a large shark, with beaches closed as drones search for the predator.

Emergency crews were dispatched to Long Reef Beach on Sydney's northern beaches shortly after 10am on Saturday, responding to reports a man had suffered critical injuries, police said.

He was retrieved from the surf and brought to shore but died at the scene.

Police have closed the beach and are liaising with wildlife experts to determine the species of shark involved.

Two sections of a surfboard have been recovered and taken for examination.

Beaches from Manly to Narrabeen have been closed pending further advice.

The identity of the man is yet to be confirmed.

Witnesses say the victim was brought ashore by two fellow surfers and that distraught family m

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