A man has been saved after spending 23.5 hours in the water at sea off Whangamatā, using the reflection from his wristwatch to catch the attention of three fishermen.

The man set off on a solo fishing trip on January 2 aboard his 40-foot boat, with the intention of returning the following day.

Near the Alderman Islands, he hooked what he suspects was a marlin, before falling overboard some 30 nautical miles (55km) off the North Island.

Unable to catch the idling boat as it meandered further out of reach, the man attempted to swim to the Alderman Islands, but was dragged away by the currents.

He endured a cold night in the ocean, too exhausted to keep swimming.

During his time in the water, even a shark came to “have a sniff”, before leaving.

Incredibly, about 2pm on Wednesday, three fishermen were on a boat near Mayor Island when they noticed an unusual reflection on the water.

They decided to investigate and discovered a fellow fisherman, desperately trying to get their attention using the reflection of the sun on his watch.

The trio plucked him from the water, immediately alerted Police and set course for Whangamatā Marina.

"It is an absolute miracle the fisherman is still alive after the ordeal," says Whangamatā Police Sergeant Will Hamilton.

"Without the quick actions of the three gentlemen that retrieved him, this certainly would have had a tragic outcome."

The man was hypothermic and exhausted when he was returned to land, where a St John ambulance crew was waiting to treat him.

"The boaties did an absolute stellar job and without a doubt saved this man’s life," says Sergeant Will Hamilton.

"In a note to Police, the man said he wanted to go on record to thank Mike, Tyler and James for rescuing him, along with all the emergency services involved."

It’s not known where the man’s boat has ended up.

The Rescue Co-ordination Centre has been advised of the last-known direction, fuel on board and speed, so navigation warnings can be issued.

Boaties are asked to report any sightings of empty powered vessels.

"Few stories end the way this one did, and Police cannot thank the eagle-eyed trio enough for making the call to investigate something that looked out of the ordinary," says Sergeant Will Hamilton.

"The boat may be missing, but the fisherman still has his watch."