A scuba diver missing for more than 17 hours off the north Queensland coast is lucky to be alive, according to his rescuers.

Key points: The 68-year-old diver did not have a personal locator beacon on his dive belt

The 68-year-old diver did not have a personal locator beacon on his dive belt He underestimated the current and was swept away from the Yongala wreck

He underestimated the current and was swept away from the Yongala wreck Rescuers were hoping the man's black wetsuit and yellow air tank would stand out against the ocean

The man, aged 68, went to dive at the SS Yongala wreck near Russell Island, south of Townsville, by himself on Sunday and failed to return.

Police were called by the man's friend about 6:45pm, and found his boat moored at the dive site later that night with no-one on board.

Rescuer Alan Griffiths was on a helicopter that had been searching for the missing man this morning for 90 minutes and was about to head back to the base to refuel when the diver was spotted about 11:00am.

"The paramedic just looked at the right angle and saw him," he said.

"There was a sense of urgency because we were heading back for fuel, but we wouldn't have been back for an hour."

Rescuer Alan Griffiths said the 68-year-old man should buy a lotto ticket. ( ABC News: Nancy Notzon )

Mr Griffiths was winched down to get the man from the water.

"I said to him, 'G'day mate, do you want a lift?'" he said.

"He said to me, 'You should buy a lottery ticket', I was like, 'No mate, you need to buy a lottery ticket'."

Mr Griffiths said the man had seen three helicopters and a plane searching for him all morning.

Rescuers were hoping to see the man's black wetsuit and yellow oxygen tank.

"He's very lucky, there is an element of luck on his side, that's for sure," Mr Griffiths said.

"Black and yellow kind of stand out."

No safety equipment and a strong current

Mr Griffiths said the man usually uses a personal locator beacon, but cleaned it several days earlier and forgot to put it in his diving box.

"He went by himself, which is a bit naughty," he said.

"He jumped in the water from his boat and then realised the current was so strong and quite simply couldn't get back to his boat.

"That's how quickly the current took him."

The man was found 10 nautical miles north east of Cape Upstart, south of Ayr.

Rescuers ecstatic the man is alive

Acting Inspector Graeme Paterson said rescue coordinators set up a search pattern from the wreck, which was calculated on the tides and currents.

"It's a huge task to search a grid pattern of the ocean," he said.

Acting Inspector Graeme Paterson said searching the ocean was a huge task. ( ABC News: Nancy Notzon )

"For police and rescue coordinators to achieve such success at this time in the day, it's a really great result."

"I imagine he'll be medically assessed to see if he is in good health condition and require any medical treatment."

Acting Inspector Paterson said the man had given clear instructions on his dive to a friend, including the location of the wreck and the time he was due back.

"Because of that, when he didn't meet his contact point yesterday afternoon the authorities were notified," he said.

Acting Inspector Paterson said calm conditions assisted the search and the man's ability to stay afloat and conserve energy.

"We're also dealing with warmer waters here so that's another thing that would certainly assist," he said.

"Every hour that somebody spends in the ocean their chances diminish so the fact that he's been found in the first 24 hours is amazing."

Six aircraft along with water police, volunteer marine rescue, the coastguard, police divers and a helicopter joined in the search this morning.

The Yongala is considered one of the best wreck dives in the world and is between 16 to 30 metres deep.