China's internet censors appeared on Tuesday to have blocked the sharing of anything but text on the popular WhatsApp social media app, amid a nationwide clampdown on mentions of late Nobel peace laureate Liu Xiaobo, who died of liver cancer in police custody last week.
Anti-censorship website GreatFire.org reported on Tuesday that the app was partly inaccessible from with the complex system of blocks, filters, and human censorship known as the Great Firewall.
WhatsApp, which is owned by Facebook and offers end-to-end encryption, isn't as popular as its homegrown counterpart WeChat among China's 731 million internet users, but has until now been more resistant to government censorship.
Social media users reported that their attempts to post banned photographs of Liu, a pro-democracy activist who wasn't treated for liver cancer until it was already at an advanced stage, had failed on WhatsApp since noon local time.
"I took photographs of a memorial event for Liu Xiaobo today," one user commented. "I was about to post them to my friends group when it just wouldn't send, not on my phone's mobile data and not on Wifi."
"I can still send out text messages though, without the need to climb the Great Firewall," the user said, in a reference to the use of circumvention tools like virtual private networks (VPNs).
The user said they had previously used WhatsApp to circumvent government censorship along with a group of more than 100 friends, who regularly used it to hold "lively discussions."
Mourning 'filtered out'
Beijing-based rights activist Hu Jia, a close friend of Liu Xiaobo and his widow Liu Xia, said the authorities are clamping down on the app, however, after successfully censoring WeChat users and content.
"At the moment, basic sentiments of mourning are being filtered out on a massive scale," Hu said. "This means that it's no longer convenient for a large number of rights activists and dissidents to use WhatsApp."
In Beijing, foreign ministry spokesman Lu Kang told a regular news briefing on Tuesday that he "has no information" on the issue.
"This isn't something that is for the foreign ministry to answer," Lu said. "You need to ask the departments that deal with communications and the internet."
Earlier this week, security researchers at the University of Toronto's Citizen Lab revealed that Chinese censors were able to intercept images commemorating Liu in private one-on-one chats on WeChat in real time, suggesting massively detailed image recognition capabilities.
According to a Chinese censorship researcher known by his pseudonym Charlie Smith, the authorities have likely implemented wholesale blocking of multimedia messages because they are unable to target the overseas-based app with the same precision.
"It would not be surprising to find that everything on WhatsApp gets blocked, forcing users in China to use unencrypted, monitored, and censored services like WeChat," Smith told the Associated Press.
The whereabouts of Liu Xiaobo's widow Liu Xia remained unknown on Tuesday amid growing calls for her release. Liu Xia has been under constant house arrest since her husband's Nobel Peace Prize was announced in October 2010, but has never been charged with any crime.
A friend of the family told RFA that they expect Liu Xia to remain incommunicado for some time, however.
"If the authorities continue to hold Liu Xia under house arrest, this would be the worst possible outcome," the friend said. "Let's wait a couple of weeks and see what happens. I am guessing that it won't be much longer than that."
The friend called on the international community to keep up the pressure on Beijing to allow her to leave the country.
"I think that if they keeping piling on the pressure, Liu Xia will eventually be allowed to leave," the friend said.
Tuesday was declared by Chinese activists as an "International Day of Mourning for Liu Xiaobo," marking a traditional weeklong period following a person's death.
Richard Choi, vice-chairman of the Hong Kong Alliance in Support of the Patriotic Democratic Movement in China, which has long campaigned on behalf of the Liu family, said activists in the former British colony would be taking part.
"We are holding a memorial event for Liu Xiaobo on Tuesday evening," Choi told RFA. "We call on the people of Hong Kong to take part, because the way the Chinese government has handled the entire affair has made people very angry."
"So we want to get large numbers of people out for this memorial, and share our reflections in this manner."
Barred from Macau
Alliance chairman Albert Ho said some pro-democracy activists in the former British colony had been denied entry to Macau, probably because they had attended a memorial for Liu in Hong Kong at the weekend, suggesting the long arm of Beijing is clamping down further on rights activists, using immigration controls.
"We have been attending memorials and openly taking part in countless public activities, and we have never been worried before, for example that we wouldn't be able to visit mainland China or Macau," Ho said.
"We are not going to take any notice of this now."
An employee who answered the phone at the border control police in Macau asked for questions to be sent via e-mail, but no reply had come at the time of writing on Tuesday.
Reported by Ding Wenqi and Qiao Long for RFA's Mandarin Service, and by Wong Lok-to for the Cantonese Service. Translated and edited by Luisetta Mudie.