Reports now suggest that China has finally gotten around to blocking WhatsApp almost completely, although a small percentage of users may still be able to use the app. The move appears to be a continuation of a larger effort from the incumbent government to disallow services and applications which it cannot easily monitor. It also follows news of a partial block from just a few months ago. That previously imposed limitation is said to have primarily disrupted audio, video, and photo services while leaving text messaging through the app in place. This time the disruption appears to be more complete and also affects texts. As mentioned above, some users may still be able to use the service through virtual private networks, connecting through servers external to the country, but the government has also been cracking down on the use of those. So there's no telling how much longer that option will be available.
The underlying goal of the crackdown seems to be in pushing users to use less secure methods for communication, such as WeChat - which has a direct link to the Chinese government, allowing users to be monitored. The disruption of WhatsApp, in particular, appears to differ from other efforts in terms of how it is implemented. Symbolic Software has been monitoring disruptions to the service, within China, since September 20. According to one applied cryptographer at Symbolic Software, Nadim Kobeissi, the disruption appears to be founded on some kind of software-based, encryption reliant method. Moreover, whatever method the country's censors are using, the disruption went from just starting out to "comprehensive" within around five days. According to Lokman Tsui, a University of Hong Kong internet communications specialist, severe disruption didn't begin until Sunday. While previous efforts to disrupt services focused mainly on imposing legal limitations to availability or simply slowing services down beyond usefulness, this appears to be the first time the country has deliberately halted a service from working outright using a software solution.
There is some speculation that the latest suspected crackdown is more generally a part of the leadup to the Communist Party congress meetings to be held in October. However, WhatsApp's parent company, Facebook, has not had any luck in working around how the Chinese government wants to regulate its telecommunications market. In fact, none of the companies other services are allowed within the country officially. Moreover, a recently reported allegation that the company had managed to get a photo-sharing application called "Colorful Balloons" into the country could feasibly be at least a small part of what spurred the new disruptions. In the meantime, the previous block was temporary and there is no way of knowing if or when the disruption will end. Facebook, for its part, has not commented on the service disruptions.