The guest of a cruise line reported missing last week, was rescued after spending more than 15 hours at sea in the Gulf of Mexico.

The unnamed 28-year-old man had been aboard the Carnival Valor cruising over the long Thanksgiving weekend.

His sister raised the alarm late on Wednesday, when he had failed to return from the toilets.

Her sibling had been missing for hours, after they had been celebrating the start of the trip at one of the ship’s bars. Now he was nowhere to be found on the ship.

Carnival spokesperson Matt Lupoli told CNN what happened next was a “Thanksgiving miracle”.

Announcements were made across the PA system throughout the ship and crew searched the ship with a photo, supplied by the missing passenger’s sister. The ship’s pool was drained and departure for the ship’s next port of call, Cozumel, was delayed.

It was shortly after 2pm on Thursday that this effort was abandoned. It was clear the passenger was no longer onboard.

The ship was turned around and retraced its course.

Coast Guard were alerted and all shipping within a 300-kilometre search area called in to help search for the missing passenger.

Then, miraculously, six hours later they spotted the missing man.

He was spotted 30 km offshore of Southwest Pass, Louisiana

It was the cargo carrier CRINIS which made the discovery and called in a Coast Guard helicopter to have the passenger winched out of the water.

Despite over 15 hours at sea he was remarkably lucid and unharmed.

“He was able to identify his name, confirmed that he was the individual that fell overboard,” Lt. Seth Gross rescue coordinator for the US Coast Guard on Friday afternoon. “He was showing signs of hypothermia, shock, dehydration,” he told CNN.

The passenger was reported missing from Carnival Valor on Thursday. Photo / Supplied, Carnival Corp

The long-serving rescue worker said it was unlike any operation he had witnessed in his 17 years.

He had never heard of someone surviving such a long stint at sea.

The unnamed cruise passenger was flown to Orleans Lakefront Airport, and spent the weekend in Hospital under medical evaluation.

Crew and passengers aboard the Carnival Valor were given the news of the ‘miraculous’ rescue via a PA announcement late Thursday evening. It continued on to Cozumel as planned.