The first flight was streamed live by Boeing with a video being tweeted of the take-off.
Boeing Airplanes (@BoeingAirplanes) January 25, 2020
The aircraft is now performing a series of air tests over Washington and can be tracked live via the Boeing Website.
The 777X is powered by General Electric GE9X engines, currently the world’s largest and most powerful commercial aircraft engines.
The 777-9, the variant due to fly, can carry up to 400 passengers while its smaller sibling, the 777-8 will carry fewer passengers but over a wider range.
At 251ft 9″ long the 777-9 is the worlds largest twin-engined airliner.