You can get an idea of what it might have been like, although at a much more modern, safe, and smaller scale by exploring the Chungking Mansions in Kowloon: http://en.wikipedia.org/wiki/Chungking_Mansions
The first half of the movie gives a really great image of the Chungking atmosphere, so definitely check it out. I highly recommend it on its own narrative strengths too of course.