Hunt for the shark ... lifesavers patrol Dee Why beach. Photo: Mackenzie Price

SEARCH and rescue teams will scour the northern beaches again after a 2.5-metre shark closed two popular swimming spots.

In the second brush with a shark on a NSW beach in the past three days, an off-duty Warringah Council lifeguard, Danny Sheather, was knocked off his board while surfing at Dee Why about 12.45pm on Sunday.

Mr Sheather did not see what hit him but noticed a 30-centimetre chunk out of the bottom of his board when he returned to shore.

"The Westpac Life Saver Rescue Helicopter spotted a 2.5-metre white shark at the southern end of Dee Why". Photo: Mackenzie Price

''It looked like something had come up and rammed him from underneath,'' Steve Downman, a Warringah Council lifeguard supervisor, said. Dee Why and Long Reef beaches were immediately closed.

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The Westpac Life Saver Rescue Helicopter soon spotted a 2.5-metre white shark at the south end of Dee Why.

Despite lifesavers' efforts it could not be moved on, so both beaches remained closed all afternoon.

''The boat attempted to shepherd the shark away from shallow water,'' Stephen Leahy, the chief executive of the helicopter service, said. ''It wasn't deterred whatsoever, which is unusual.''

More here:

Beaches closed as shark refuses to be herded off