SYDNEY (AFP) - A diver separated from his boat off the coast of Australia said on Sunday (Oct 22) he was lucky to be alive after being forced to swim miles back to shore - shadowed by a large tiger shark.

The spear fisherman, named in local media as Mr John Craig, was underwater off Western Australia state near Shark Bay on Friday when his boat was swept away due to engine problems and strong currents.

"I was trying to splash and scream and shout to get my friend's attention," he told BBC Breakfast. "All of the splashing, I could feel my heart rate up because I was panicking that I had been left, and after about five or 10 minutes of this, I just put my head in the water to check I was still in the same place, and then at arm's reach there was this huge 4-metre tiger shark."

"It was at that moment I realised, I have just got to forget about the boat and go totally into survival mode," said Mr Craig, who is from Sunderland.

"It was easily the biggest tiger shark I've been in the water with and that's saying something, having worked as a dive instructor for over 10 years."

Mr Craig said a sandbar whaler was also closing in on him in the shark-infested waters near Shark Bay as he made the decision to swim back to shore.

"I have to admit that at this point I thought I was gone - four nautical miles out to sea with a huge tiger shark following me. I thought this was it, this is how I'm going to die," he said.

"I just kept my head in the water, watched what the big tiger shark was doing, and it kept coming back towards me. It would circle me and kind of dart in and I just had to use my spear gun to try and fend it off and try and keep it at a safe distance," he recalled.

"The shark would disappear into the gloom then suddenly reappear behind me, just keeping pace with me behind my fins."

Eventually, Mr Craig was spotted from the air and picked up by a boat from the Shark Bay Volunteer Marine Rescue.

Tiger sharks are ranked second only to the great white in terms of attacks on humans, according to the International Shark Attack File from the Florida Museum of Natural History, reported The Guardian.

Mr Craig said of the experience, "... as much as it was scary at the time, I can only reflect on how beautiful that big female tiger shark was."

"It's an absolutely incredible story," Shark Bay Volunteer Marine Rescue commander Greg Ridgley told Perth's Sunday Times.

"He swam at least five miles in shark-infested waters... I just can't believe anybody could do that. It's such a massive effort, in that short timeframe too."

There have been 14 encounters off the nation's vast coastline this year, including the death of a 17-year-old girl mauled by a shark in full view of her parents in Western Australia.

Experts say incidents are increasing as water sports become more popular and baitfish move closer to shore, but fatalities remain rare.