Switzerland's Viking River Cruises is expanding its fleet further with another order in Germany.

The Torstein Hagen-chaired company has contracted seven new river ships that will debut in 2019, the Neptun Werft shipyard said, without revealing a price.

Six of the vessels are Viking Longships for operation on the Rhine, Main and Danube Rivers, while the other is inspired by the Longships and specifically designed for Portugal’s Douro River.

Viking will operate a fleet of 69 river vessels around the world by 2019. The group will also have six ocean-going vessels.

“We knew there was an opportunity to do things differently when we started this company 20 years ago,” said Viking chairman Hagen.

“In the last two decades, we have spent more than $1bn marketing the concept of river cruising to North Americans, and today we are a household name.

"The Viking way of exploration has resonated with our target audience of experienced travelers, and this new ship order is a reflection of strong demand for more destination-focused cruises.”

The Longships will accommodate 190 passengers in 95 staterooms.

They feature energy-efficient hybrid engines that also reduce vibrations.

Neptun delivered a series of 10 river ships to Viking in 2015 and 2016.