The United States Coast Guard was searching early on Friday for a 26-year-old man who went overboard from a Carnival Cruise ship about 76km (47 miles) out in the Gulf of Mexico, near the port of Galveston in Texas.
A spokeswoman said the coastguard was preparing to launch a search-and-rescue cutter after midnight, with more than 10 of its crew having joined the initial stages of the search.
A helicopter and a fixed-wing aircraft manned by divers and rescue equipment, including a hoist to lift a person out of the water, are also being deployed in the effort, she added.
The ship, Carnival Dream, started a four-day cruise from Galveston on Thursday, the cruise operator Carnival Corp said.
“Based on camera footage, it appears the guest jumped from his stateroom balcony,” it said in a statement.
The 14-deck vessel can accommodate more than 3,600 passengers in more than 1,800 cabins, internet cruise tracking site Ship Technology said.
No further information from the coastguard or the cruise line was immediately available.