Solar Impulse 2, which is attempting to fly between Japan and Hawaii powered only by the sun's energy, has broken a world record for the longest non-stop solo flight.

The plane is expected to land in Hawaii by 4 July, shattered the solo-flight record threshold of 76 hours while crossing the Pacific on 2 July.

Piloted by Swiss explorers Bertrand Piccard and Andre Borschberg, Solar Impulse took off on its 22,000-mile (35,000-km) journey around the world from Abu Dhabi on 9 March.

"Can you imagine that a solar powered airplane without fuel can now fly longer than a jet plane!" Piccard was quoted by Reuters as saying. "This is a clear message that clean technologies can achieve impossible goals."

Solar Impulse 2
Swiss pilots Andre Borschberg (L) and Bertrand Piccard (R) of Solar Impulse 2, the world\'s only solar-powered aircraft. Getty

The round-the-world flight was expected to take some 25 flight days, broken up into 12 legs at speeds between 30 to 60mph. However, it was forced to cut short its initial bid to traverse the Pacific due to what Borschberg termed "a wall of clouds".

After landing in Hawaii, Borschberg and Piccard will fly Solar Impulse from Honolulu to Phoenix, Arizona, and then across the Atlantic to return to Abu Dhabi.

"The experience of flight is so intense that I can only focus on the present moment and discover how to deal with my own energy and mindset," Borschberg said in a statement.