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."
"Over the next few days, we will get a much better sense of how much of this is reaching mainland China," Michael Auslin, resident scholar at the American Enterprise Institute, told NBC News.
At least some information is getting through, according to Reuters, but information about the Hong Kong protests remains heavily censored, including on the popular messaging app WeChat and search site Baidu.
"Beijing wants these protests to peter out over the next few days," Auslin said. "They want for the protesters to say, 'Hey, we made our point, we had thousands of people in the streets, and now it's time to go home.'"
If the protests keep going strong, Beijing might have to get more involved. That could include telling Hong Kong police and public officials to shut down access to social media and possibly even the Internet itself.
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That may be one reason many protesters seem to be turning to an app called FireChat. More than 100,000 people in Hong Kong downloaded the messaging app between Sunday morning and Monday morning, according to Open Garden, the company behind the app.
The FireChat app allows users to create a mesh network of phones through their radio and Bluetooth signals, a web of connected devices. That means no Wi-Fi or cellular signals are needed to communicate if China decides to cut off Internet access completely — a measure that, while extreme, has been taken before in other areas of the country.
The worst-case scenario for the Communist Party, Auslin said, is that dramatic photos and messages make it through the "Great Firewall" and inspire similar protests in mainland China. That could force Beijing to do something more drastic.
"Their first preference is not to send in the Liberation Army, because they will destroy the fiction of an independent Hong Kong," Auslin said. "They want the Hong Kong government and Hong Kong police to take care of this."
Hong Kong's status as a global economic hub has mostly protected the city's Internet from censors since it was handed back to the Chinese by Britain in 1997.
The city's Internet runs on an independent infrastructure that, along with making it more difficult to control from Beijing, has the added benefit of providing the third fastest broadband speeds in the world. That does not mean, however, that Hong Kong activists feel safe when it comes to speaking out online.
"China would love to gain more control over the Internet in Hong Kong," Earp said. "That is one thing these protests are really about — the encroaching presence from mainland China."