General view during the delivery ceremony of the Harmony of the Seas (Oasis 3) class ship at the STX Les Chantiers de l'Atlantique shipyard site in Saint-Nazaire, France, May 12, 2016. [Photo/Agencies]

2,500 workers have spent 10 million work hours to complete the vessel since September 2013

The world's biggest-ever cruise ship, the 120,000-ton Harmony of the Seas, a luxury home on the waves for 8,500 passengers and crew, was handed over by a French shipyard on Thursday after a 40-month engineering feat.

At 66 meters, it is the widest cruise ship ever built, while its 362-meter length makes it 50 meters longer than the height of the Eiffel Tower.

The floating town, which cost close to one billion dollars, has 16 decks and will be able to carry 6,360 passengers and 2,100 crew members.

The ship was built for US-based Royal Caribbean Cruises Ltd by the STX France boatyard in Saint-Nazaire on the Atlantic coast, where a spectacular ceremony marked the handover on Thursday.

"It's not only the biggest cruise ship in the world, it's also the most expensive ever built," said Richard Fain, head of the cruise company, at a ceremony which featured blaring music and tightrope walkers performing splits over the aquatheater at the back of the ship.