Unless you are bound and determined to "walk on the wild side" and expereience some of the seamier elements of Chinese cities, you will have absolutely no problem with personal security as a western visitor. Tourist $ and business investment are too valuable to Chinese government/society for problems to be tolerated.
Now, if you are an ethnic Chinese visitor, again finding yourself in the wrong place at the wrong time, your personal security odds go down a bit. Too easy to mistake you for a local, or worse yet a rich Chinese diaspora visitor.
Often read of HKers visitng Shenzhen getting into trouble. Rare to read of white westerners having problems, unless htey asked for them.