China has blocked WhatsApp (that is owned by Facebook), so in case you are planning to visit China and have been using WhatsApp before do note that Whatsapp will be inaccessible in China from now on.
However it seems WhatsApp has been blocked for China based users or if you use China based SIM / their network. This means that if you have international SIM card and if you have activated data roaming on your SIM then you may still be able to use WhatsApp.
It is not just Whatsapp, Facebook, Gmail, Google services have already been blocked in China. In China WeChat is mostly used that is also monitored by the Chinese Government. If need be Chinese govt could have monitored WhatsApp but it seems that the strong security feature that provides encryption for end to end users may be the reason, that way even Whatsapp does not know what is being sent.
Anyway if you travel to China frequently do note that Whatsapp has been blocked. It makes sense to enable your data (international roaming / international data pack) that way there is a high chance you may be able to use Whatsapp and other services that have been blocked in China.
Source : BBC