China on Thursday extended a massive censorship operation to target popular social media sites, banning keyword searches linked to the 1989 Tiananmen Square military crackdown 25 years ago and a mass vigil in Hong Kong's Victoria Park, netizens said.
Keywords like "June 4, 1989" and "6.4" are often blocked to China's 620 million Internet users, who often find ever more ingenious ways to elude censorship, however.
Netizens have used terms such as "Something Something Square" and "May 35th" to get around the blocks and filters, although "May 35th" began to be blocked for the first time last month.
The ruling Chinese Communist Party's powerful but secretive central propaganda ministry issued censorship instructions to the country's tightly controlled media recently, ordering editors to avoid any reference to June 4, or 1989.
"All websites are asked to strengthen on-duty work during this time of highest sensitivity," the leaked directive, collated and translated by the China Digital Times website, said.
"Closely observe reporting discipline. Ensure that a responsible editor is always present," it said.
"Strictly delete information about overturning the official line and commemorating June 4 (including so-called sideways expressions)," the directive said.
It warned: "We stress once again the responsibility of websites to check content. Anyone found to be violating discipline during this inspection will be severely punished."
It singled out a post that had appeared on the Tencent entertainment channel headlined "Amnesiacs: How can we save you?" which in some versions appeared with the numbers 6 and 4 in the headline.
Hong Kong vigil
State-run media on Thursday was silent on a massive candlelight vigil attended by at least 100,000 people in Hong Kong on Wednesday to mark the crackdown.
And the list of blocked search terms had expanded on Thursday to include "Victoria Park", "candlelight," and "Teng Biao," the name of a leading Chinese human rights lawyer who delivered a swingeing attack on the Chinese government at the rally.
On the popular Twitter-like service Sina Weibo and similar social media sites, censors quickly located and deleted posts containing the banned terms.
And users of the popular chat service QQ said many of their groups were shut down in recent days.
"A lot of chat groups were shut down and disbanded," online activist Hua Manlou, who is currently on enforced "vacation" under police escort outside his hometown, told RFA.
"It was mostly the ones talking about people being 'disappeared,'" he said. "There were about six or seven groups shut down."
Social media activist Wu Gan, known online by his nickname "The Butcher," said controls this year were far tighter than anything seen before.
"They began cracking down on WeChat and QQ at the beginning of the year, but they stepped this up further by June, across the board," Wu said.
"It's been a bit different this year compared with previous years; they are getting a lot more pro-active in their campaigns."
"It seems that the future trend is in this direction," Wu added. "It's getting harder and harder to send out tweets, but they can't lock it down entirely because people's desire for information is getting stronger and stronger."
He said many more netizens were taking the trouble to use software to circumvent the complex systems of blocks, filters, and human censorship known as the "Great Firewall."
"More and more people are going over the wall, so as to use certain sites aimed at freedom."
Typically, searches for blocked content in China return a message apologizing for the non-delivery of search results "in accordance with relevant laws, regulations, and policies."
However, the official news agency Xinhua did make some oblique reference to the events of June 1989 in order to hit back at international condemnation of the crackdown on dissidents and rights activists in the run-up to the anniversary.
Chinese foreign ministry spokesman Hong Lei once more defended Beijing's handling of the crackdown, using almost identical language to previous official comments on the topic.
"On the political upheaval in Beijing, the Chinese government long ago reached its conclusion," Hong told a regular news briefing in Beijing. "In the last 30 years of reform and opening up, we have made remarkable economic progress."
Reported by Yang Fan for RFA's Mandarin Service. Translated and written in English by Luisetta Mudie.