A man has died on a Sydney beach after being bitten by a suspected "large shark", Australia's New South Wales police have said.

In a statement, the police said emergency services pulled the man out of the morning surf onto the shore at Long Reef Beach - but he "died at the scene".

"Two sections of a surfboard have been recovered and taken for expert examination," the statement read.

Saturday's incident has resulted in a string of closures in the popular area known as the Northern Beaches.

The state police said the emergency services acted after receiving reports shortly after 10:00am local time on Saturday (00:00 GMT) that "a man had suffered critical injuries".