When experienced diver John Craig found himself alone in deep water more than seven kilometres off the WA coast — and with a four-metre tiger shark circling him — he thought those moments might be his last.

His dive partner was in their boat, but engine trouble saw it swept away while Mr Craig was underwater off Shark Bay on Friday afternoon.

A major air and sea search for Mr Craig was launched and his family and friends feared the worst while the light faded over the waters, known to be heavily populated with sharks.

"I just thought about my wife and how worried she'd be," said John Craig. ( Supplier: John Craig )

Mr Craig, 34, said the incident was sparked by a series of unfortunate events which began when he was free-dive spear fishing at his last dive spot for the day.

His spear became stuck under a rock and by the time he was able to get it out, the boat with his dive partner on board was like a dot on the horizon.

'My heart rate was sky high'

"I had been splashing and screaming for some time and my heart rate was sky high," he said.

"After five minutes it was clear I was on my own.

"I put my head in the water to check I was in the same place and suddenly saw a huge four-metre tiger shark approaching within arm's reach.

"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.

"Its head was nearly a metre wide, it was about three times the girth of me and it was just like a submarine just circling.

"I quickly turned and saw another large sandbar whaler circling behind me and it was at that point I decided to give up on getting to the boat and save myself."

Mr Craig believed it was probably attracted by his panicked splashing and he knew had to try and calm down to survive.

'I thought I was gone'

Mr Craig said the tiger shark began circling and making sudden darts towards him.

John Craig swam for three hours, careful to keep any splashing to a minimum. ( Supplied: John Craig )

He managed to keep his speargun between them, but was careful not to touch the shark and risk provoking it.

"It was definitely trying to work out what I was and whether I could be on the menu," he said.

"After about two minutes of this dance I thought I have to get out of here and started swimming for shore.

"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."

The shark eventually gave up and Mr Craig decided to head in the direction of the remote Peron National Park cliffs, which were barely visible on the horizon.

For three hours he swam, careful to keep any splashing to a minimum.

"By the time I got to the beach I was exhausted. I could barely stand, my legs were so sore from the 7.5-kilometre swim."

Rescue crews in the distance

When he stood up he saw dozens of boats in the distance searching for him, and a plane overhead but did not see him.

John Craig believes his panicked splashing around attracted the tiger shark. ( Supplied: John Craig )

Unable to raise their attention Mr Craig began walking along the remote stretch of coast to a campsite five kilometres away.

He said he desperately wanted to let his wife, Emma, know he was OK.

"I just thought about my wife and how worried she'd be. I just wanted to tell her I was alive," he said.

The sun was almost down when the pilot of the search plane made his last pass for the day closer to the coast.

Mr Craig ran out into the middle of the beach waving and screaming and he knew the pilot had seen him.

He said relief swept over him when he saw a fisheries boat racing towards him.

"Sergeant Kev Pierpoint looked like Daniel Craig as he waded through the shallows to meet me."

Mr Craig said after arriving back in the town of Denham, the next stop was the local pub to celebrate with the Volunteer Marine Rescue crews, police and the dozens of local boat owners who had been part of the search.

"For a small town in regional WA it just shows what great community spirit is all about," he said.

"I am eternally grateful and I'm sure I'll be buying beers for years to come."

Humans 'not on the menu'

Mr Craig has been a dive instructor in Shark Bay for a number of years and said although he was concerned for his safety under those circumstances he has not had issues when he has swam with sharks under more controlled conditions.

"These animals are apex predators but we are not 'on the menu'," he said.

"We need them in the oceans, as much as it was scary at the time.

"If the circumstances were different I would have been stoked to have that experience."