Hong Kong, China - In the early hours of June 4, 1989, soldiers from China's People's Liberation Army (PLA) converged on the few protesters remaining in a smoke-filled Tiananmen Square. The confrontation with students and citizens left hundreds or even thousands of people dead, and thousands more injured.

This week, as the world commemorates the 25-year anniversary of the Tiananmen Square crackdown, Beijing has been working ever harder to obscure the digital record of the event.

"We started to notice some problems with Google's [Internet properties] last week and it soon became clear the authorities had decided [to] block the sites entirely," said an anonymous representative of GreatFire.org, a group that charts Internet censorship in China. By Tuesday morning, the organisation tweeted a photograph from Google's own transparency report, tacitly confirming that "All Google services in all countries, encrypted or not, are now blocked in China".

While censorship in China is not new, the decision to disrupt access to the Internet giant represents a serious escalation in the battle to control access to information on the mainland.

"This is by far the biggest attack on Google that's ever taken place in China," a co-founder of GreatFire.org told The New York Times. The obstruction, which has impeded access to Google's search function as well as its images service, Gmail, maps and translation tools, was followed by reports that the Wall Street Journal's news sites, in both English and Chinese, had also been turned off.

"Google services have been throttled frequently over the past few years," said Jeremy Goldkorn, the director of Danwei, a company that tracks China's media and Internet space. Tensions have grown since Google closed down its mainland China search engine rather than censoring user searches, as Beijing demanded. This past March, after revelations of the US National Security Agency's spying sparked calls for increased privacy and user protections, Google instituted automatic encryption for all searches, limiting Beijing's ability to censor specific material.

To block users from accessing information the government was eager to hide, officials were forced to shut off the flow entirely, Internet freedom advocates reported.

"Internet users in China have almost come to expect these sorts of disruptions surrounding the June 4 anniversary," said Jason Ng, a Google policy fellow at the University of Toronto's Citizen Lab and author of Blocked on Weibo, a book about China's popular Twitter-like service. Ng remembers similar Internet protocols during the 20th anniversary of Tiananmen, when users lost access to Twitter, Hotmail and the self-publishing platform Blogspot. Internet analysts labeled it "Internet maintenance day".

'Heavily censored'

Last year, Ng published a study investigating words banned on Sina Weibo, known as China's Twitter. At that time, flagged phrases included "Tank Man", "Tiananmen incident" and "June 4," in addition to allusions to the events, such as "square", "pillar of shame" and "April 65th" - terms still used to circumvent online censors.

"Over the past few years we've seen a better understanding by users that the Chinese Internet is heavily censored," Goldkorn said. "With the growth of Weibo and the time people spent on the site, it became clear that certain material was disappearing."

According to a report published last year by Reuters news agency, 150 censors work for Weibo - mostly college-aged males - and represent a small fraction of the untold thousands employed to sift through content in both traditional and digital media.

"[Chinese President] Xi Jinping, like his predecessors, is on [a] futile mission to control discussions about Tiananmen and broader issues," said Sophie Richardson, China director at Human Rights Watch, in a press release last week. The government's search for control led to the arrest of five attendees of a "June 4 Commemoration seminar", held in a private home, on charges of "creating a public disturbance". Foreign ministry spokesman Ma Zhaoxu has officially stated that "there are no dissidents in China".

Nevertheless, a new generation of Internet users is developing tactics to push back against the Chinese state, which was ranked third-to-last in the most recent Freedom on the Net report published by Freedom House, a watchdog group.

GreatFire, the non-profit organisation monitoring censorship in China, has boasted multiple successes "hacking" through firewalls on behalf of users. Soon after China's moves against Google this week, the group created a mirror site, shielded in the cloud computing infrastructure hosted by Amazon web services. Through a protected web address, users from mainland China could gain access to encrypted and untainted Google searches.

"For China to stop our site, they would have to block access for every user or company that hosts with Amazon," a GreatFire representative who wished to remain anonymous told Al Jazeera. "But this would cause severe economic damage, for individual leaders and their families." Less than two days after erecting the mirror page, more than 20,000 visitors had used the service, GreatFire told Al Jazeera.

And GreatFire isn't alone.

Temporary freeze?

GoAgent, a popular anti-censorship tool in China, uses Google cloud services to ensure that government attempts to block the system are "technically feasible, but economically disruptive". As of June 3, however, GoAgent's Google hosting page had been blocked for users in mainland China.

Whether this week's measures are permanent or temporary remains unclear.

"Based on past history and the potential for netizen anger, I don't expect the block to last much longer after June 4," said Ng, citing the yearly tensions associated with the Tiananmen Square anniversary.

What is clear, however, is how little companies like Google can do in response.

"The only arrow in their quiver is that a lot of Chinese companies use Google's advertising platforms to generate revenue," said Goldkorn, who also believes the freeze will be temporary as "so many government officials probably use Gmail".