Cruise line officials are trying to figure out how two passengers managed to fall at least 50 feet from a ship's balcony into the Gulf of Mexico Sunday, where they were rescued hours later.
"You cannot just fall off a ship," said Princess Lines' spokeswoman Julie Benson, describing the occurrence as "extremely rare ... this hasn't happened to Princess, that I can recall."
The 22-year-old man and 20-year-old woman -- who have not been identified publicly other than as Americans -- fell at about 1:30 a.m., 150 miles from Galveston, Benson said.
They were recovering Sunday with minor injuries in the medical center aboard the Grand Princess, a spokeswoman for Princess Cruises told CNN.
"They're being watched and treated for their injuries," which include hypothermia from the 71-degree water, Benson said.
In addition to being extremely rare, the outcome of the incident was "extremely lucky," Benson said.
Falling 50 to 60 feet into water is itself "rather treacherous," she said. The fact that the two fell into pitch-black water roiled by sea swells, current and wind made the incident even more dangerous, she said.
"It appears, at the moment, that it was just a terrible accident, and there was nothing sinister about it," she said, adding it was not clear whether the two had known each other prior to the voyage or how they both fell.
They were reported missing after their friends "heard screams" and discovered the two were missing, a passenger said the ship's captain had told him.
"When alerted to this, the ship stopped, initiated an emergency search operation, and returned to the position where the overboard incident was initially reported," Benson said, adding that the ship turned around and headed back within 10 minutes of getting word.
"Rescue boats were launched from Grand Princess, and the U.S. Coast Guard was notified," she said.
Capt. Ed Perrin, a Briton with some 20 years experience, "turned around rather immediately" and attempted to retrace his path, taking into account such variables as current and wind, Benson said.
At 5:30 a.m., after four hours in the water, the woman was found and pulled from the water by the crew of a rescue boat that had been lowered from the cruise liner; a half hour later, the man was rescued, she said.
Neither had been wearing a life jacket, she said.
The two passengers remained on board as the ship continued toward a scheduled stop Monday in Costa Maya, Mexico. The nearly five hours lost to the search were made up "just by increasing the speed," Benson said. "The ship will be maintaining its original schedule."
The Grand Princess, with 2,783 passengers and 1,122 crew, departed Galveston on Saturday afternoon for a week-long voyage through the western Caribbean.