The sun-powered Solar Impulse 2 aircraft has set off from New York's JFK airport, embarking on the transatlantic leg of its record-breaking flight around the world to promote renewable energy.
The flight, piloted by Swiss adventurer Bertrand Piccard, is expected to take about 90 hours - during which Mr Piccard will only take short naps - before landing at Spain's Seville airport.
"It's my first time taking off from JFK," Mr Piccard said over a live feed from the aircraft as he headed into the night sky.
The voyage marks the first solo transatlantic crossing in a solar-powered airplane, and is one of the most difficult legs in Solar Impulse 2's journey around the world.
#Si2's cockpit is now closed, here I go for 4 days alone over the #Atlantic without a drop of fuel! #futureisclean pic.twitter.com/OMvPG0n5Xo
— Bertrand PICCARD (@bertrandpiccard) June 20, 2016
The plane, which is no heavier than a car but has the wingspan of a Boeing 747, is being flown on its 35,000km trip by two pilots taking turns - Mr Piccard and Swiss entrepreneur Andre Borschberg.
The pair have alternated legs of the journey, with Mr Borschberg piloting the flight's final Pacific stage, a 6,437km flight between Nagoya, Japan and Hawaii.
The 118-hour leg smashed the previous record for the longest uninterrupted journey in aviation history.
The plane, now on the 15th leg of its east-west trip, set out on 9 March 2015 in Abu Dhabi, and has taken the aircraft across Asia and the Pacific to the United States with the sun as its only source of power.
Smooth takeoff and all #Si2 systems have been checked here at the Mission Control Center for the #Atlantic Crossing pic.twitter.com/W6CQ82APtF
— André Borschberg (@andreborschberg) June 20, 2016
Prince Albert of Monaco, a patron of the project, gave the flight the go-ahead from its mission control centre in Monaco, telling Mr Piccard "you are released to proceed."
A third of the journey still remains for the plane, which will fly through Europe and on to the Middle East back to Abu Dhabi after crossing the Atlantic.
The single-seat aircraft is clad in 17,000 solar cells. During night-time flights it runs on battery-stored power.
It typically travels at a mere 48km/h, although its flight speed can double when exposed to full sunlight.
The two pilots are no strangers to adventure.
Mr Piccard, a psychiatrist, made the first non-stop balloon flight around the world in 1999.
Meanwhile, Mr Borschberg only narrowly escaped an avalanche 15 years ago and in 2013 survived a helicopter crash with minor injuries.
