The world's largest twin-engine plane has completed its first test flight, landing safely near Seattle.

Boeing claims its 777X jetliner uses 10% less fuel and can accommodate either 384 and 426 passengers, depending on the model.

Saturday’s flight comes as a potential image boost after the American company's 737 Max planes were suspended last year following the Lion Air crash in October 2018 and the Ethiopian Airlines disaster just five months later.

The 777X flew in Washington State, completing a near-four hour trip from Everett to Seattle, the day after adverse weather conditions prevented an earlier take-off.

“The 777X flew beautifully, and today's testing was very productive,” said Captain Van Chaney, 777/777X chief pilot for Boeing Test & Evaluation.

The plane’s larger size will allow for a more spacious cabin, according to Boeing, larger overhead compartments, windows and better cabin altitude.

Boeing expects to deliver the first 777X in 2021.

The program, the company claims, has won 340 orders and commitments from carriers around the world, including ANA, British Airways, Cathay Pacific Airways, Emirates, Etihad Airways, Lufthansa, Qatar Airways and Singapore Airlines.

Boeing claims the plane is 10% more fuel-efficient. Credit: Boeing

Former Boeing chief executive Dennis Muilenburg was sacked in December last year, in a move the firm says was intended to “restore confidence in the company”.

The two 737 Max crashes killed everyone on board, a total of 346 people.

In October, an Indonesian investigation into the Lion Air flight found that it was doomed by a combination of aircraft design flaws, inadequate training and maintenance problems.

Angle-measuring sensors in both planes are known to have malfunctioned, alerting anti-stall software to push the noses of the planes down.

The pilots were unable to take back control of the aircrafts in both cases, leading to the crashes.