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If it is not urgent, you may ask someone (family member or friend) in US to express mail the old pasport to HongKong. If it is too urgent, you may just ask your family member in US to scan  the information pages of the old passport including the Chinese Visa page and entry and depature pages into/out of China, and then email the pages of the old passport above to you (I am not sure whether it works, but it deserves to try with explain it to the Chinese Customs Officer if you do not have other choice)..