General view of the theatre 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]

'Extraordinary feat'

"Creating this ship in 40 months is an extraordinary feat - it's the achievement of thousands of people," said Laurent Castaing, head of STX France.

Harmony of the Seas will produce 20 percent less CO2 emissions than the next two largest ships in its class, partly thanks to air pumped into the hull to lighten its load.

It took 2,500 workers at STX France around 10 million work-hours to complete the enormous vessel after work began in September 2013.

The contract marked a major boost for the boatyard after several lean years.