According to the story several hundred people saw this over China. Is this a mirage? A Reflection? Blue beam? Or a rip in dimensions? If that was the case why would there be a city in the sky(Doc brown ala Back to the future pop's in my head, "Your not thinking 4th Dimensionally") Perhaps there is an overlay of worlds or dimensions and perhaps positioning so we might be seeing is of another world or parallel earth but just in a different position in spacial terms. Who knows but it is quite interesting.
Edward