Strange lights over Pudong, Shanghai?

On May 29th, 2011, I saw some strange lights in the sky from my apartment building in Shanghai. There were four lights in all that seemed to hover and move slowly in a non-consistent pattern. The lights themselves flickered between red and green, but they all seemed to blink at different speeds. I thought that I might simply be observing aircraft landing at the Pudong airport, but this seems unlikely as the four lights seemed to linger for far too long to be commercial airliners. As I've stated before, I was watching them from my balcony facing the Huangpu River (facing east) and looking towards the site of the Shanghai expo. Are these lights from a building? What are they? I'm not the type to jump to conclusions, so I'll leave it to the Yahoo Answers community to give insight (especially if you saw the same thing and are wondering the same thing I am).