BEIJING — There is no Twittering about Tiananmen Square, or anything else, in China this week.
In a crackdown apparently timed to the 20th anniversary Thursday of the crushing of pro-democracy demonstrations, the Chinese government has pulled the plug on the social networking site Twitter and dozens of other Internet sites and blogs.
Not to neglect the old-fashioned methods of censorship, foreign newspapers sold in Beijing in the last few days have had pages strategically ripped out. Television screens in the diplomatic compound went black when the British Broadcasting Corp. was airing a report about Tiananmen Square, only to come back on when reports switched to the missing Air France jet.
"They feel this is a fragile time for China," said artist and activist Ai Weiwei, whose popular blog was shut down by authorities over the weekend.
Even though two decades have elapsed, the demonstrations remain one of the most sensitive subjects in China. The very mention of the date June 4 (when the People's Liberation Army moved in to crush the demonstrations) is banned in the Chinese press.
Police have also detained writers, activists and former dissidents who participated in the 1989 protests. Others have been put under surveillance or house arrest, barred from traveling to Hong Kong, where a demonstration Sunday marked the anniversary.
Ding Zilin, whose 17-year-old son was killed in the crackdown and who now heads the group Tiananmen Mothers, was told to leave Beijing until the anniversary passed, said the New York-based group Human Rights in China.
At least one participant in the demonstrations two decades ago, Wu Gaoxing, has been taken without explanation into police custody from his home in Zhejiang province. Wu, who spent two years in prison for his role, was one of five authors of an open letter to President Hu Jintao complaining of the continued mistreatment of former prisoners from the Tiananmen era.
The government appears fearful that activists will stage a demonstration to commemorate June 4, as is happening in cities outside China.
Besides Twitter, which went down Tuesday, Hotmail's Web-based e-mail and the photo-sharing site Flickr have been blocked. YouTube has been blocked here since early April.
Jeremy Goldkorn, an expert in online media in China, said he thought the government was particularly upset that people were trading information about how to gain access to a controversial memoir that has just been published. It was written by the late Zhao Ziyang, the former secretary-general of the Communist Party who was fired in 1989 for his opposition to the military crackdown on the demonstrations.
The Chinese government routinely raises what is nicknamed the "Great Firewall of China" at times of political sensitivity.
It has also canceled conferences and speeches around this period. A musician who was scheduled to give a radio interview Thursday about the cultural scene in Beijing said he was told by the station that it had to be canceled because of "technical difficulties."
"The host apologized and explained there is a rash of technical difficulties arising all over the country on Thursday," said the musician, who asked not to be named.