Norwegian Cruise Line chief executive Andrew Stuart is leaving the helm of the US cruise major after three decades with the company.

Harry Sommer, president of International for parent entity Norwegian Cruise Line Holdings, will replace Stuart at year's end.

The Frank Del Rio-led holding company declined to say why he was leaving but said the "planned departure" follows recent launch of 3,889-berth Norwegian Encore.

Norwegian Cruise Line Holdings did not immediately return an email asking why Stuart was stepping down or if Sommer's current role will be filled.

Stuart will remain with Norwegian Cruise Line as senior advisor through 31 March 2020 to ensure a smooth transition, Norwegian Cruise Line Holdings said.

“I could only have dreamed about my journey at Norwegian when I joined the company in 1988 and am extremely fortunate to have witnessed firsthand the incredible evolution of this pioneering brand,” Stuart said in a statement.

He has held several key executive positions at Norwegian Cruise Line since joining the brand in 1988, including president and chief operating officer.

He has also served as executive vice president of global sales and passenger services; executive vice president and chief product officer and executive vice president of marketing, sales and passenger services.

Stuart's accomplishments with Norwegian Cruise Line include introducing its Freestyle Cruising that frees passengers from traditional set dining times and venues.

“Andy has accomplished everything possible in the cruise industry, including leading its most storied and innovative brand," Norwegian Cruise Line Holdings chief executive Frank Del Rio said in a statement.

"He will leave on a high note after delivering the brand’s latest ship, Norwegian Encore, the last ship in the most successful ship class in the company’s history."

Del Rio said Norwegian Cruise Line Holding has worked for several years on a succession plan to find Sommer as the right person to fill Stuart's shoes.

"The board and I are confident that Harry is the right person to succeed Andy as president and chief executive officer of the Norwegian Cruise Line brand and look forward to him leveraging his breadth of knowledge and extensive experience in the industry and our Company to take the brand to new heights.”

As president of International for Norwegian Cruise Line Holdings, Sommer is responsible for sales, marketing, public relations and office operations outside of US and Canada for Norwegian Cruise Line and its sister brands Oceania Cruises and Regent Seven Seas Cruises.

“Andy and I have worked closely together over the last several years and I am humbled and honored to follow in his footsteps and lead this renowned brand,” he said in a statement.

“I look forward to working with all of our incredible partners worldwide, building off the strong position the brand holds today and charting the strategy for the next phase of Norwegian’s journey.”

His previous roles with Norwegian Cruise Line Holdings include previously executive vice president of international business development and executive vice president and chief integration officer.

Norwegian Cruise Line Holdings' shares declined 1.8% to $48.26 by late morning Thursday.