Rescuers have found a "needle in a haystack", plucking a scuba diver out of the Coral Sea more than 50km from where he went missing after he spent more than 18 hours in the water overnight.

The 68-year-old man, who was lost at sea off the north Queensland coast overnight, is counting his lucky stars today while recovering from mild hypothermia in Townsville Hospital.

He had been at the SS Yongala wreck dive site, 20km off Cape Bowling Green, yesterday afternoon but failed to return.

The solo diver was found by a rescue helicopter this morning more than 50 kilometres southeast of the popular dive site.

Air Rescue Officer Alan Griffiths said it appeared he didn't realise how strong the current would be around the Yongala wreck, where divers normally visit in groups.

"He's gone by himself, which is a bit naughty. He jumped in the water from his boat and then realised the current was so strong and he simply couldn't get back," Officer Griffiths said.

The lost diver was found this morning after more than 14 hours at sea. (Supplied)

The diver is winched to safety. (Supplied)

A friend who knew his dive plans alerted police about 6.45pm yesterday, prompting a massive air and sea search.

Acting Inspector Graeme Patterson said it was a huge task.

"It's like looking for a needle in a haystack," he told reporters today.

The man suffered mild hypothermia but is otherwise unharmed. (Supplied)

Searchers found the man's boat at the dive site before 9pm last night but there was no sign of him.

He was eventually spotted in the water about 18 hours later waving to the rescue helicopter and winched to safety.

Mr Griffiths said the diver, who was not using his personal locator beacon, had seen three helicopters and a plane searching for him earlier in the morning.

"He was very, very lucky," the rescue officer said.

“He was happy to see us.”

“I went down to him and swam over and said ‘G’day mate, want a lift!’”

"He said to me 'you need to buy a lottery ticket', and I said 'No, you need to buy a lottery ticket'.