The Police rescue helicopter was being flown for the purpose of conducting the search for and rescue of a seriously injured rock fisherman in the MacMasters Beach area, south of Terrigal. It departed Bankstown at about 0555 ESuT and arrived at the command post at Little Beach at about 0620. Shortly after, a paramedic was embarked and a search initiated. The injured person was located about 650 metres south of the command post. The helicopter was flown back to Little Beach, where a crewmember disembarked and returned to the location of the injured person. It then was landed on a nearby rock ledge near the waters edge, where both the paramedic and the observer left the helicopter to assist the fisherman. The helicopter then took off and moved away to minimise noise and rotor wash in the immediate area. The pilot reported that at that time the wind was calm, the visibility unlimited, and there was some wave action against the lower of two rock shelves. He asked the ground party by radio if a 'Stokes' litter was required for the retrieval of the fisherman, but was advised by the paramedic that this would be unnecessary as the fisherman could be carried down to the rock shelf, close to the original landing point. The helicopter was brought to a low hover to allow the patient and observer to board. After receiving a clearance to depart from the paramedic, who remained on the ground, the pilot commenced a takeoff. At a skid height of about 12 ft above the rock shelf, the entire aircraft was engulfed by a very large wave. The takeoff was aborted and the helicopter was stabilised in a hover. Almost immediately, it was struck by a second wave, resulting in a double engine flameout. The helicopter was landed on the rockshelf, where it was then struck by a third wave, which rolled it onto its side and forced it against a low rock face. After the helicopter had come to rest, all three persons on board were able to escape, assisted by the paramedic. The pilot reported that the sea state then returned to its original, relative calm. However, after a further 80 minutes, another series of very large waves struck the helicopter, resulting in further damage. Significant Factors 1. Deceptive sea state. 2. Desirability of rescuing injured person with minimum delay.