With freezing temperatures in the country’s capital, Beijing and similar temperatures in Shanghai, travelling to China in December means bringing lots of warm clothes and especially thermal underwear! Lows in Beijing can reach -10 with it only being slightly warmer in Shanghai.
In central and south China, while it’s not as cold, the damp cold can be just as bone-chilling. December is usually not a great month for China travel as most of the north is too cold for being outside at great lengths of time. If you are looking for a beach escape, the far south such as tropical Hainan Island is a good destination for some heat and sun.