A Western Australian board rider says he was hit “like a freight train” in a terrifying shark encounter that he somehow managed to survive.

Andy McDonald, 61, was wing-foiling at the back of a surf break at Margaret River in WA’s south-west on Monday afternoon.

“Just out of the blue, something just went [bang], straight up from behind, like a super solid hit and I was flying through the air and just crashed into the water,” he told the Seven Network.

In another interview, McDonald said after he was propelled from his board, he fell on top of the shark.

“I just started punching it,” he told the ABC.

“It sort of dragged me underwater, and dragged the board and the sail under.

“I thought, ‘Well, this is it.'”

Andy McDonald was wing-foiling when he was attacked. Photo: Seven Network

McDonald was about 700 metres from shore as he tussled with the ocean predator in a fight for his life, fearing that “I was gone”.

The incident was captured by the Swellnet surf camera.

“It was obviously biting my board, and then it dragged me under the water, took me under, dragging the board and the sail,” he told Seven.

“This is it. I’m so far out to sea, no one’s around, there’s no jet-skis or anything and I’m at the mercy of this beast.”

He eventually broke free and was able to clamber on top of his sail, trying to remain as calm as possible. He admits he “lost the plot a bit” and started screaming for help.

Bravely, his friend Neil Mattinson, who was about 50 metres away, could see something was going on — initially thinking McDonald had injured himself on the wing foil — and paddled over to help.

“It was an incredible effort [from Mattinson] because I didn’t know if the shark was still around,” McDonald told ABC.

The splash when Andy McDonald was dragged under was caught on the Swellnet surf camera. Photo: Swellnet

The pair made the 20-minute paddle back to shore where it became obvious from the 350-380-millimetre bite mark in McDonald’s board that he had just survived a shark attack.

Apart from that piece of evidence, McDonald said he never actually saw his animal attacker. But he estimated it was as long as 3½ metres.

“Even when I was underwater, didn’t see it. I might have seen a flash of colour — there was so much foam and kicking and I was punching it as well, and kicking it, trying to keep all my arms and legs intact, I didn’t know where its head was,” he said.

Authorities issued a shark warning for Prevelly in the Shire of Augusta Margaret River.