SHANGHAI — China has largely blocked the WhatsApp messaging app, the latest move by Beijing to step up surveillance ahead of a big Communist Party gathering next month.

The disabling in mainland China of the Facebook-owned app is a setback for the social media giant, whose chief executive, Mark Zuckerberg, has been pushing to re-enter the Chinese market, and has been studying the Chinese language intensively. WhatsApp was the last of Facebook products to still be available in mainland China; the company’s main social media service has been blocked in China since 2009, and its Instagram image-sharing app is also unavailable.

In mid-July, Chinese censors began blocking video chats and the sending of photographs and other files using WhatsApp, and they stopped many voice chats, as well. But most text messages on the app continued to go through normally. The restrictions on video, audio chats and file sharing were at least temporarily lifted after a few weeks.

WhatsApp now appears to have been broadly disrupted in China, even for text messages, Nadim Kobeissi, an applied cryptographer at Symbolic Software, a Paris-based research start-up, said on Monday. The blocking of WhatsApp text messages suggests that China’s censors may have developed specialized software to interfere with such messages, which rely on an encryption technology that is used by few services other than WhatsApp, he said.