With the anniversary of the Tiananmen Square crackdown on Thursday, China's ever-vigilant censors have stepped up the reach of the "Great Firewall," blocking Western sites like Twitter, Flickr, and (just one day after its launch) Microsoft's Bing.

 The measures came as the authorities tried to close all avenues of dissent ahead of Thursday's anniversary, placing prominent critics under house arrest and banning newspaper from making any mention of the pro-democracy protests.

The co-ordinated internet "takedown" occurred at 5pm local time (10am GMT) on Tuesday as a broad range of websites suddenly became unavailable to Chinese internet users[...]

Foreign newspaper and television channels were also subject to censorship as the highly sensitive anniversary approached.

Viewers of the BBC's world channels in Beijing found their screens turning black whenever reports on the anniversary were being aired and four foreign television crews attempting to film in Tiananmen Square reported being stopped by police.

Print publications were also affected, with many subscribers to The Economist magazine receiving their weekly copies with the Tiananmen-related pages ripped out. Readers of the Financial Times and South China Morning post also reported missing pages.

As for those who saw the expanded censorship coming, the "Surprisingly Accurate Internet Claim" award goes to Chinese blogger Michael Anti, who just last Wednesday told Danwei.org:

"Twitter is a new thing in China. The censors need time to figure out what it is. So enjoy the last happy days of twittering before the fate of Youtube descends on it one day."

If there's one group who respond quickly to news, though, it's Twitter users, who have already made the topic one of the most talked about on the site. After all, as one user put it: "No Twitter in China now? How do they make it through the day?"

FREDERIC J. BROWN/AFP/Getty Images