Going through the customs and declarations

I expect to be flying between the US and China a few times this year. I am also preparing a shipment (personal belongings) by seas since I will spend most of my time in China in the near future. I am wondering when I take my flight to China and go through the customs, do I need to declare things I am sending by ship as well? As I may take the second flight before the seas shipment arrives in China, I am wondering when (the first flight or the second flight), if required, I should inform the customs about the packages I carry with me by air as well as by seas.