Social media among Hong Kong protesters pose a "nightmare scenario" for Chinese censors, experts say, while apps meant to evade a further electronic clampdown in the city have surged in popularity.
The Communist Party has blocked access to the photo-sharing service Instagram in mainland China as massive protests continue in Hong Kong, protesters and reporters based in the city have said, according to Reuters.
Instagram declined to comment in response to a request from NBC News.
Beijing already routinely blocks access to YouTube, Twitter and Facebook on the mainland. Pro-democracy phrases, especially those connected to the "Occupy" movement, have been banned on China's Twitter-like micro-blogging service Sina Weibo.
"For China, it's the usual reaction in the face of any demonstration," Madeline Earp, research analyst at Freedom House, told NBC News. "Facebook, Twitter, you name it, it tends to be blocked the minute it's used for political mobilization in China."
The unrest started as Hong Kong residents demanded fully democratic elections after Beijing announced only government-vetted candidates would be allowed to run for chief executive of the city in 2017.
Containing the fire
Hong Kong itself is mostly free from the "Great Firewall of China" that censors social media, although some search terms and references to sensitive events are occasionally banned. Within the city, Instagram users can still post and look at images. Their global followers can also get a glimpse of the action.
Beijing might not be too happy with people in Hong Kong and the United States seeing these images, but, according to Earp, they are more concerned about them spreading to mainland China.
"From the point of the view of the censors, this is a nightmare scenario," she said. "We saw exactly the same thing in 2011 when the Arab Spring began to gain traction. Images of people massing in public squares in the Middle East were very concerning. They feared that it would spread and be seen as a possibility for Chinese activists."