As the ruling Chinese Communist Party ramps up security ahead of this week's 25th anniversary of the 1989 crackdown on pro-democracy demonstrators around Beijing's Tiananmen Square, the authorities are also targeting any attempt to commemorate or address the bloodshed online.
And authorities in the southern Chinese province of Guangdong have detained an online activist who launched an online essay competition commemorating the crackdown, a Chinese rights group reported.
Police in Chaoshan in the eastern part of the province are holding Zhang Kunle under criminal detention on suspicion of "picking quarrels and stirring up trouble," China's Weiquanwang website said.
"The bloody history of June 4, 1989 remains in memory! Instead of hating, we should analyze and understand this event from a social science perspective," Zhang wrote in a statement announcing the contest.
"There should be no hatred or biased viewpoints, and I will treat those who write well to a huge meal of Chaoshan congee ... and some chilled Qingdao beer," he wrote.
Zhang's friend and fellow activist Jia Pin said the charges against Zhang were illegal and unreasonable.
"He has been a pro-democracy activist in Shenzhen for a long time now, and they have come down very hard on him since he organized some meals [for fellow activists] in Shenzhen in recent months," Jia said.
"[After that], Zhang Kunle went back home to his hometown for a while."
He said that of the dozens of activists detained in the run-up to the 25th anniversary on Wednesday, 13 were in Guangdong.
"This is unreasonable, and illegal," Jia said. "But everyone knows that mainland China has no rule of law to speak of right now."
"There is nothing in law that mentions an online essay competition," he added.
Rights groups say at least 50 people have been detained ahead of the anniversary, with many more confined to their homes under surveillance or escorted away from them by state security police on enforced "vacations."
Meanwhile, Google's search services appeared to be blocked to many users in China beginning last week, according to censorship watchdog GreatFire.org.
Government censors appeared to have begun targeting Google's main search engine and Gmail, among many other services, since at least last week, making them inaccessible to many users in China, the group said in a blog post on Monday.
"It is not clear that the block is a temporary measure around the anniversary or a permanent block," the group said.
"But because the block has lasted for four days, it's more likely that Google will be severely disrupted and barely usable from now on."
A Google spokesman told Reuters: "We've checked extensively and there's nothing wrong on our end."
Google's publicly available global traffic report showed lower levels of activity from China starting from about Friday.
Google left China in 2010 after a showdown with the government over Internet controls and currently redirects Chinese language users from the mainland to a search site run from its Hong Kong-based servers.
China's complex system of blocks and filters already ensure that popular foreign websites like Facebook, Twitter and YouTube are hard to access for the majority of its 600 million Internet users.
China's leadership has ignored growing calls for a reappraisal of the 1989 student protests, which the party has styled a "counterrevolutionary rebellion."
The number of people killed when PLA tanks and troops entered Beijing on the night of June 3-4, 1989 remains a mystery.
Beijing authorities once put the death toll at "nearly 300," but has never issued an official toll or list of names, and has always maintained that the violence was necessary to end the unrest.
Reported by Yang Fan for RFA's Mandarin Service. Translated and written in English by Luisetta Mudie.