The smokestacks of the Oasis of the Seas had to be lowered to allow the ship's passage under a bridge in Denmark. (Royal Caribbean/Associated Press)

The world's largest cruise ship cleared a crucial obstacle Sunday, lowering its smokestacks to squeeze under a bridge in Denmark.

The Oasis of the Seas — which rises about 20 storeys high — passed below the Great Belt Fixed Link with a slim margin as it left the Baltic Sea on its maiden voyage to Florida.

Bridge operators said that even after lowering its telescopic smokestacks the giant ship had less than half a metre of clearance.

Hundreds of people gathered on beaches at both ends of the bridge, waiting for hours to watch the brightly lit behemoth sail by shortly after midnight (2300GMT; 7 p.m. EDT).

"It was fantastic to see it glide under the bridge. Boy, it was big," said Kurt Hal, 56.

Company officials are banking that the massive vessel's novelty will help guarantee its success. Five times larger than the Titanic, the $1.5 billion ship has seven neighbourhoods, an ice rink, a small golf course and a 750-seat outdoor amphitheatre.

Can carry 6,300 passengers

It has 2,700 cabins and can accommodate 6,300 passengers and 2,100 crew members. Accommodations include loft cabins with floor-to-ceiling windows, and 1,600-square-foot (487-meter) luxury suites with balconies overlooking the sea or promenades.

The liner also has four swimming pools, volleyball and basketball courts, and a youth zone with theme parks and nurseries for children.

Oasis of the Sea, nearly 40 per cent larger than the industry's next-biggest ship, was conceived years before the economic downturn caused desperate cruise lines to slash prices to fill vacant berths.

It was built by STX Finland for Royal Caribbean International and left the shipyard in Finland on Friday. Officials hadn't expected any problems in passing the Great Belt bridge, but traffic was stopped for about 15 minutes as a precaution when the ship approached, Danish navy spokesman Joergen Brand said.

Aboard the Oasis of the Seas, project manager Toivo Ilvonen of STX Finland confirmed that the ship had passed under the bridge without any incidents.

"Nothing fell off," he said.

Tropical theme aboard $1.5 billion vessel

The enormous ship's various "neighbourhoods" feature parks, squares and arenas with special themes. One of them will be a tropical environment, including palm trees and vines among the total 12,000 plants on board. They will be planted after the ship arrives in Fort Lauderdale.

In the stern, a 750-seat outdoor theatre — modelled on an ancient Greek amphitheatre — doubles as a swimming pool by day and an ocean-front theatre by night. The pool has a diving tower with springboards and two 10-metre high-dive platforms. An indoor theatre seats 1,300 guests.

One of the "neighbourhoods," named Central Park, features a square with boutiques, restaurants and bars, including a bar that moves up and down three decks, allowing customers to get on and off at different levels.

Once home, the $1.5 billion floating extravaganza will have more, if less visible, obstacles to duck: a sagging U.S. economy, questions about the consumer appetite for luxury cruises and criticism that such sailing behemoths damage the environment and diminish the experience of travelling.

Oasis of the Sea is due to make its U.S. debut on Nov. 20 at its home port, Port Everglades in Florida.