Hapag-Lloyd Cruises is to order a third new cruiseship as demand increases.
Parent TUI has approved a deal for a vessel to be delivered in 2021, it said.
Hapag will shortly launch the planning and negotiation process for a further Hanseatic-class ship, it added.
"Due to the continued rise in demand, TUI is planning to expand the segment through additional newbuilds," it said.
The first two vessels in the series, the 16,100-gt Hanseatic Nature and Hanseatic Inspiration, are due from Vard Langsten in April and October 2019, respectively.
They will join the five other cruiseships in the Hapag-Lloyd fleet.
TUI said its cruiseship division remained on a growth path in the six months to 31 March.
"The positive trends and forecasts for the next few years have also been confirmed by current growth rates," it added.
Underlying EBITA was up 23.2% at EUR 92.4m ($109m).
The average rate per passenger per day for TUI Cruises was EUR 148, up from EUR 147; for Marella Cruises it was £136 ($183) from £127; and for Hapag-Lloyd Cruises EUR 600, against EUR 595 in the previous year.
