Beijing turned up the volume on the "Great Firewall of China" Tuesday, blocking nearly a dozen Western Web sites and search engines.
Thursday is the 20th anniversary of the Tiananmen Square massacre, and as a foretaste, Chinese users were denied access to Blogger, Flickr, Twitter, Livejournal, Tumblr, the Huffington Post and Microsoft's Live.com, Hotmail, its MSN Space blog tool and its new search engine Bing, according to various reports.
"Looks like Twitter has been GFWed in China," tweeted Mimi Xu, or @MissXu, a Hong Kong-based tech entrepreneur who noticed she wasn't getting responses from mainland friends, using the common Twitter acronym for "Great Firewall of China."
The block of YouTube, which began in March after Tibetan activists posted clips, according to London's Guardian newspaper, continued.
"The 3 web services I cant live without — Twitter, Flickr, YouTube — are all blocked in China," tweeted Stephen Lin, a Chinese blogger who tweets as @flypig.
Some third-party Twitter desktop clients were working, letting users get around the block, but others were down.
"This is so frustrating. Now I feel China is exactly the same as Iran," wrote one financial professional in Shanghai, according to Reuters.
A State Department spokesman declined to chastise the Chinese government for any crackdown on Internet access or other attempts to control coverage of this week's events.
However, spokesman Robert Wood said human rights are always an element of the relationship with China.
"Obviously, concerns about freedom of speech, expression, assembly, [are] something that's of great concern to the United States, everywhere in the world," he said.
The Times of London noted that Twitter had let Chinese users write terms that are blocked on Web sites, such as "6/4" for the date of the Tiananmen massacre or "Charter 08" for a well-known pro-democracy dissident manifesto.
"Twitter is a new thing in China. The censors need time to figure out what it is," blogger Michael Anti told another Chinese blog last week, according to the Times. "So enjoy the last happy days of twittering before the fate of YouTube descends on it one day."
"I want to point out that the Chinese Twitterland is funnier than the English one, for a Chinese tweet can have three times the volume of an English tweet, thanks to the high information intensity of the Chinese language," he added.
Twitter limits users to 140 characters per "tweet," but in Chinese one or two characters can make up an entire word.
Two former targets of Chinese ire — Google and Wikipedia — were apparently not affected. Nor were Facebook or MySpace.
"Since Bing.com is blocked in China while Google.com is not, is it implying that Google is doing better Gov Relations than MS?" wondered Lin.
Britain's Daily Telegraph noted that "old" media was also being subjected to Tiananmen-related measures.
BBC World viewers in China saw TV screens go black when reports on the anniversary were aired, and pages were cut out of the Economist magazine and Financial Times and South China Morning Post newspapers.
The BBC reported that prominent dissident Wu Gaoxing, a leader of the 1989 democracy movement, was arrested over the weekend and was still being held.
China has said that 241 people were killed in the Tiananmen Square crackdown. Unofficial estimates of deaths range from 400 to 5,000.