Solar Impulse 2 has taken off from Myanmar's second biggest city of Mandalay and is heading for China's Chongqing, the fifth flight of a landmark journey to circumnavigate the globe powered solely by the sun.
The single-seater aircraft's team spent more than a week waiting in Mandalay for weather conditions to improve in southwestern China, before finally taking off early on Monday, for what will be one of the most challenging legs of the round-the-world attempt so far.
Speaking on a live feed from mission control in Monaco, Prince Albert gave pilot Bertrand Piccard clearance for takeoff.
"Bertrand, from Albert, you are clear to proceed. Have a nice flight," Prince Albert said.
"Thank you very much my friend," Piccard replied before taking off at around 3:35am local time (2105 GMT on Sunday) into the dark pre-dawn skies.
Piccard, one of the two Swiss pilots of the solar-powered plane, will have to battle extreme cold of down to 20 degrees below zero in the cockpit and the general unpredictabilities of flying above the mountainous Chinese provinces of Yunnan and Sichuan.
Flying at a high altitude for most of the journey, Piccard will also need to use additional oxygen.
The 1,375km route is expected to take around 18 hours.
The team behind Solar Impulse 2, which has more than 17,000 solar cells built into its wings, hopes to promote green energy with its circumnavigation attempt.
Ridiculed by the aviation industry when it was first unveiled, the venture has since been hailed around the world, including by UN chief Ban Ki-moon.
Muscat was the first of the 12 planned stops on the plane's maiden journey from Abu Dhabi, with a total flight time of around 25 days spread over five months.
From Oman the plane flew to the Indian city of Ahmedabad before heading to Varanasi and then Mandalay.
From Chongqing it will depart for the eastern coastal city of Nanjing before embarking on the most arduous leg of its journey, an 8,172km, 120-hour odyssey across the Pacific to Hawaii.