Swimmer missing in wild surf off Sydney

A man is feared missing in dangerous surf in Sydney's north.

Rescue helicopters, lifeguards and emergency service workers are at Turimetta beach near Warriewood after witnesses reported a swimmer in trouble.

"A number of witnesses have reported that a male swimmer was seen to be floating on the surface of the surf and was seen to be hit by a dumping wave and hasn't resurfaced," Westpac Life Saver Rescue Helicopter chief executive Stephen Leahy told AAP.

Mr Leahy said a NSW Ambulance helicopter, Pittwater Council lifeguards, police and ambulance officers were at the scene.

Turimetta Beach is just south of the notorious Warriewood blowhole, where a teenage boy had a lucky escape on Wednesday.

The 14-year-old was rescued by lifeguards from a ledge inside the blowhole tunnel after falling from rocks.

Mr Leahy said conditions were dangerous right along the Sydney coastline, with large surf prompting warnings from the lifesavers and the Bureau of Meteorology.