The ships – each worth €800 million – will accommodate around 3,300 guests, and are scheduled for delivery in 2022, 2023, 2024 and 2025.

The additional two ships could then be delivered in 2026 and 2027.

Parent company Norwegian Cruise Line Holdings said the new class of vessels would build on the line’s most recent Breakaway –Plus class ships and would feature “innovative designs”.

It added that a “priority of the prototype design” was energy efficiency, with the aim of "optimising fuel efficiency and reducing [the ships’] impact on the environment".

More details of the new features will be announced at a later date.

Frank Del Rio, president and chief executive of Norwegian Cruise Line Holdings Ltd said: "This new class of ships will continue Norwegian Cruise Line brand’s legacy of introducing meaningful innovation to the cruise industry”.

"This order continues to highlight our disciplined newbuild program, extends our growth trajectory well into the future, enhances our already attractive earnings profile, and drives expected long-term returns for our shareholders."