A surfer who was knocked unconscious by a whale at Sydney's Bondi Beach on Sunday morning says he feels lucky to be alive.

Bishan Rajapakse, 38, was surfing with a friend when a whale "the size of a bus" surfaced close to the beach around 10:30am (AEST).

Mr Rajapakse says when he paddled over to take a look, he noticed the whale directly underneath him and woke up later on the sand.

"The whale actually moved pretty quickly so I guess it's made me cautious to see what could happen," he said.

"[I know] it's better to look at them from afar [but] it's pretty hard to move away from that temptation, because I guess the whale was looking so placid."

Mr Rajapakse is being treated in St Vincent's Hospital for head and shoulder injuries.

Bishan Rajapakse says he feels lucky to be alive. ( ABC News: Lucy Carter )

Witness Lachlan Harris says the whale appeared to be frolicking with the surfers.

"They were playing and the whale was frolicking with them and having a lot of fun and sort of popping its head out," Mr Harris said.

"It just flicked its tail and some surfers were in the wrong [place] and the next thing you know a surfboard is flying in the air [and] swimmers are getting thrown out of the water. It was unbelievable.

"What a dinner party story for the surfer. How many people get beaten up by a whale on an average Sunday morning? Not that many I don't think."

New South Wales Ambulance Service spokesman Adam Wallace says the incident was an unusual one for paramedics.

"They do experience a lot of things in their role but I will suggest that whales at Bondi Beach is not the sort of thing that paramedics see everyday," he said.

Paramedic Kristie Sky, who treated Mr Rajapakse at the scene, said it was the strangest call out she had ever had.

"I've been a paramedic for 12 years and this is by far the most interesting case and way out that I've ever done," she said.

"Everyone that's... heard the story, they're all pretty amazed by it as well."