If you’re planning to explore China in winter (December, January and February), you can expect it to be anything from chilly to freezing, depending on where you are. Be sure to pack warm clothes for sleeping (thermals are a good idea), thicker socks and at least two lightweight fleeces (in case one gets wet) even if you’re travelling in the south. Even in areas like Yangshuo, temperatures in January can drop to around 6°C (43°F) at night.
If you’re travelling in the interior or north of China during winter, you should pack all of the above plus a few extra thermal layers, warm gloves, a scarf, waterproof shoes and a warm jacket. Remember that it’s not unusual for Beijing temperatures to drop to -8°C (18°F) in the middle of winter and Xi’an sometimes get snow in January.