"The flight is going really well, I have just flown over Liege, it's a real pleasure to enter Belgian airspace," Andre Borschberg said as the dragonfly-like aircraft cruised at 50 kilometres (31 miles) per hour.

"The view I have here is extraordinary," the Swiss pilot added in a live feed over the Internet. "I'm above the clouds, for now I'm taking advantage of the blue sky."

The experimental emissions-free aircraft was scheduled to take just over 12 hours to cover some 480 kilometres (300 miles) from western Switzerland to Brussels airport, after flying over France and Luxembourg at 3,600 metres (11,880 feet), the Solar Impulse team said earlier.

The single seater lifted off gently in clear blue skies from Payerne airbase at 8:40 am (0640 GMT) after being delayed by early morning mist.

Solar Impulse HB-SIA, which has the wingspan of a large airliner but weighs no more than a saloon car, made history in July 2010 as the first manned plane to fly around the clock and through the night on the sun's energy.

It holds the endurance and altitude records for a manned solar-powered aeroplane after staying aloft for 26 hours, 10 minutes and 19 seconds above Switzerland, flying at 9,235  metres (30,298 feet).

The high-tech plane has since flown several times, notably between Geneva and Zurich airports, but the journey to a busy airport at Brussels through crowded airspace is regarded as a new test.