My first trip to Hong Kong was in July. As I recall, the temperature was 35C and 90% humidity most days. Unbearable. Add to that a wool suit and you were going from walking down the street, getting soaked with sweat, to walking into a near-refrigerated office (everyone seemed to keep there offices extra cold), and getting blasted with a wave of cold that seemed to instantly freeze that previously mentioned layer of sweat into a fine icy film. Having said that, China is not HK and the climate varies greatly. Shenzhen in the south is the same climate as HK (being directly across the border). Shanghai in August will probably be more like New York. Still hot, but more bearable. Regardless of where you are, most Chinese are fairly casual so suits are typically not required. Particularly if you are the customer. What kind of suppliers are you meeting with? Most manufacturing is quite casual, so you can wear slacks and a shirt. I wear jeans, because our factories tend to be very casual.
You also need to take into account your own corporate image. If you are representing a major company, you may need to dress up to your corporate policy. Even then, though, a suit is probably not needed. I used to bring buyers and executives from the largest retailers in the world on factory tours, and slacks and short sleeves or golf shirts were the standard for them.
Make sure you book some down time if you can. China is a beautiful country and there is a lot to see. At least that's what others tell me. I personally just count the minutes until I can get to Hong Kong, which is my safe preferred destination in that neighbourhood.
Rob's bare essentials: Mama Bear, Astra SP, Slim Adjustable, TGN Silvertip