An Australian surf skier has admitted that he is lucky to be alive after he was attacked by a shark in seas north of Perth.

Martin Kane, 62, was thrown into the water after the shark bit his surf ski, off Mallaloo Beach.

He described the attack like being hit by "steam train" and says he heard a loud bang and a crunching noise.

"I just didn't know what happened basically and the next thing I know, I'm in the water. It was an almighty crash, almighty bang," Kane told reporters.

He was shaken but not injured, and was rescued by a fellow skier.

"I thought 'I was gone, I'm dead, this is just, am out of here.' I thought there was no way I'm going to make it back to the beach with that size shark after me," Kane said.

There have been four fatal shark attacks in the Western Australia state since September last year.