US-based shipping line Viking Cruises has placed an order to purchase seven new river ships, which are expected to be launched in 2019.

The order includes six new Viking Longships, which will be designed to serve the company’s existing routes on the rivers Rhine, Main and Danube in Europe.

The remaining contracted vessel will be inspired by the Longships class with further customisation for operation on Portugal’s Douro River.

Viking's latest order is expected to bring the company's fleet of river vessels to a total of 69 units.

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

“In the last two decades, we have led the industry to define what modern river cruising looks like today.

"We continue to lead the industry with the largest fleet, the widest selection of itineraries and stateroom categories, and the most awards of any river cruise line.

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

Viking further noted that each of its six new Longships vessels will be equipped with a patented corridor design and an all-weather indoor / outdoor Aquavit Terrace that is designed to bring the panoramic outdoor river scenery indoors with retractable floor-to-ceiling glass doors, among other features.

The ships will comprise 95 staterooms each and be able to accommodate 190 passengers.

The vessels will also feature two Explorer Suites, seven two-room Veranda Suites, 39 Veranda Staterooms with full-size verandas and 22 French Balcony Staterooms.

Additionally, Viking’s new ship for Portugal's Douro River will be developed to carry 106 passengers in 53 staterooms.

The vessel will join Viking’s existing fleet of three ships currently serving Douro River following delivery.