It was a heart-stopping moment fit for the pages of Moby Dick.

As kitesurfer Dave Sheridan skimmed across the choppy waters off Valla Beach, on the NSW north coast, he failed to see a giant shadow gliding centimetres below the surface.

Until, that is, the tale of a southern right whale flicked up from the whitecaps and whipped him on the back of the head.

"I thought I was gone," Mr Sheridan, 42, was quoted by the Daily Telegraph as saying.

"It all happened so fast that all I could do was crouch down as the whale swam under me ... Next thing I felt was its tail come up and hit me."

The amazing encounter took place 100m from shore on October 26 and was recorded by the camera Mr Sheridan keeps mounted on his kite, 25m above the water.

The camera, which shoots frames every 10 seconds, missed the tail-flicking drama but did capture the moment when the mammal turns its huge grey body directly beneath the kiteboard.

The southern right also proved to be less aggressive than Mr Sheridan feared, with its tail flick apparently meant only as a warning.

"It was more of a push than a punch," Mr Sheridan was quoted as saying. "The force eased off and I sailed away with shaking legs."

A whale expert said the mammal’s reaction was typical of southern rights.