The world’s biggest cruise ship was launched yesterday when its milestone float-out ceremony took place.

The 220,000-tonne leviathan, called Oasis of the Seas, is being built by American company Royal Caribbean at the STX Europe shipyard in Turku, Finland.

The 1,187ft vessel, that can carry 6296 passengers, is so big that its exhaust stack retracts so it can pass under bridges as it travels the world.

Representatives from the owners and the shipyard turned a wheel to let the water into the enormous dry dock where the 65% finished vessel is still being built.

It will take around 15 hours to fill the dock as it needs 87 million gallons of water to float the ship.

The £700 million vessel is 40% bigger than any other cruise ship afloat and it has a Central Park-style open-air space aboard the size of a football field with its own micro-climate. The world-first attraction means that guests can have the option of a sea or tree view.

In addition there is a bar called Rising Tide that will move between three of the 16 passenger decks.

Completing the major new attractions is a 750-seat AquaTheater concept, modelled on an ancient Greek amphitheatre, located at the stern of the ship.

It allows guests onboard the chance of lounging around the biggest pool afloat in the day and then going back at night for shows including |acrobatics, synchronised swimming and professional high-diving.

Other amenities include loft-style apartments and an ice rink, plus the usual pools, restaurants and a casino.

The ship, which will be completed next year, is family-friendly, with activities including surf machines and a climbing wall as the company tries to lure younger people to cruise.