Two employees were thrown into the water when high winds caused the Carnival Triumph to break free in the Gulf Coast port of Mobile, Alabama, where it was docked after a hellish four-day ordeal last month.
Television pictures showed a large hole on the stern of the ship, apparently on a passenger deck half way up the side of the vessel.
All Triumph employees were accounted for, but one non-Carnival worker remained missing, said Carnival, which has suffered a string of accidents since its cruise ship the Costa Concordia capsized off the Italian coast last year.
"Due to strong winds that reached speeds exceeding 70 miles per hour [113km/h] during a severe storm ... Carnival Triumph, which was in wet dock at a Mobile shipyard, broke away from its moorings," said a Carnival statement.
"The ship drifted, and was secured. With the assistance of tugboats on site, the ship has been moved to the Mobile Cruise Terminal. Lines have moored the ship, and, as a precaution, tugboats will remain alongside the vessel as well."
Update
About 600 crew and 200 contractors on board were safe and accounted for, with no reports of injuries. "While assessment of damage to the ship is ongoing, initial indications suggest the damage is limited," it said.
But in a 19:00 (2300 GMT) update on the afternoon incident, it cited reports that two shipyard employees on an adjacent pier fell into the water.
"One has reportedly been rescued by the US Coast Guard and the search continues for the second. Our thoughts and prayers are with the missing shipyard employee and the family," it said.
The Triumph docked in Mobile last month, after an engine room blaze left the massive vessel without electricity to power the kitchens, toilets, and other necessities for four days.
The incident comes two and a half weeks after another Carnival ship, the Legend, suffered a problem with a unit that affects its sailing speed, and had to scrap a visit to Grand Cayman.
Around the same time another troubled ship, the Dream, was finishing a Caribbean cruise when it suffered a mechanical issue with a diesel generator. Power was not lost, but elevators and restrooms periodically lost electricity.
Thirty-two people died when the Costa Concordia smashed into rocks off Tuscany in January last year, keeling over with 4 229 people on board.