A mother recounted how she watched with terror as her son was attacked by a shark yesterday - but managed to fight it off. 

Elizabeth Osborne was watching the final of the World Surfing League's J-Bay Open when the shark circled her son Mick Fanning,

Fanning fought off the predator with his fists before returning safely to shore. 

She said she feared the worst for her son.

"I just couldn't believe what I was seeing, really. I saw this sort of fin, big fin and then Mick sort of scrambling and sort of turning around and then he went down, and I realized then it must be a shark attack and I was absolutely terrified. I thought we'd lost him," she said.

Her first thought was to try and save her son.

"I jumped up and ran to the telly thinking, am I seeing this, and really, the thought went through, I have to pull him out, just like a child, you know. You feel as if you have to have to pull him out of the water. But of course that was really unrealistic, but that was my first instinct, to get him out of there," Osborne said.

She said the worst moment for her was when she lost sight of Fanning as a wave blocked the view of the television camera and she wasn't sure where he was.

"Very, very scary. I think that was the most scariest part because when he was fighting or splashing I knew he was there but when that wave came up and we couldn't see him, I just thought, oh my God, you know, where is he, is he okay, has he gone under, and then you are waiting for the boat and it seemed to take so long but then saw him swimming so that was such a relief," she added.

Fanning, three-times world surfing champion, was paddling out to ride his first wave when the unidentified species of shark surfaced next to him, knocking the 34-year-old off his board.

The Australian managed to fight off the predator, hitting it on its back before it swam off, leaving him shaken as he waited for a support boat to return him safely to shore.

The World Surf League said the J-Bay Open has been called off after the incident. With no winner, Fanning and fellow finalist Julian Wilson opted to split the event prize money.

South Africa's waters are among the most shark-infested in the world. A swimmer was killed by a Great White shark at Albatross Point close to Jeffrey's Bay in 2013.