"People were jumping out of the balloon from about the height of a seven-storey building, " Cherry Tohamy, an Egyptian who was in another balloon, told the BBC.

BBC: Egypt balloon crash: Two Britons and UK resident die

Unlike a conventional hot air balloon where the height is controlled by a burner, the gas balloons are filled with hydrogen and controlled by releasing gas to go down and throwing out ballast to go up.

BBC: Wiltshire

Finally, at a height of almost 19km, the balloon burst and the payload fell back to earth helped along by a parachute.

BBC: Giant weather balloon carries out its sky mission