Due to intense crosswinds across mainland China, the sixth flight of Solar Impulse 2, from Chongqing to Nanjing, has been delayed a second time.

The pilots were expected to fly last week, however due to less than ideal weather conditions, the flight was delayed.

Although presented with a chance to fly on Thursday, as crosswinds subsided momentarily during the night, the team decided the window for clear weather was too short, making the flight too risky.

For the sixth leg of the trip, Bertrand Piccard, one of the two pilots and co-founder of Solar Impulse, is set to fly the zero-fuel airplane for about 1,200 kilometres over about 20 hours.

During their standby in Chongqing, Mr Piccard has been training for the cross-Pacific flight, which is scheduled for next month. The plane will travel from Nanjing to Hawaii on a five-day non-stop flight.

Andre Borschberg, the other pilot and the chief engineer of the project, has travelled to Switzerland for medical check-ups and is expected to be back with the team next week.

Solar Impulse 2 took off from Abu Dhabi on March 9 in an attempt to circumnavigate the globe without using a dro of fuel.