Several Chinese Internet sites and parts of popular Web portals went offline Tuesday amid tightening controls that have already left mainland Web users without access to Facebook, Twitter and other well-known social networking sites.
China stepped up its crackdown on social networking sites in March over online allegations surrounding the treatment of Tibetans, and the blockages continued through the 20th anniversary of the Tiananmen Square demonstrations and the recent ethnic riots in Xinjiang.
The harsh measures are also thought to be part of efforts to ensure social stability ahead of the 60th anniversary of communist rule on Oct. 1, when Beijing will mark 60 years of communist rule.
Digu and Zuosa, two Chinese Web sites that offer micro-blogging services similar to Twitter, were both shut down for maintenance, according to notices posted on their homepages. A Digu spokeswoman who would only give her surname, Zhang, said the site was offline so it could be moved to a new server. She said it would be down for at least a week.
"It's a sensitive period, so we are not in a rush to re-open it," Zhang said, adding that some Digu users had recently tried to post politically sensitive material to the site and that the company was having to censor such content. She wouldn't give any specific examples.
Zuosa employees did not respond to an e-mail seeking comment about the sites' closure.
The technology channels of the popular Sina and Netease Web portals were also shut, apparently because they had posted news about a corruption probe without clearance from state censors.
China, with the world's largest population of Internet users at more than 298 million, has the world's most extensive system of Web monitoring and censorship and has issued numerous regulations in response to the rise of blogging and other trends.
While the government claims the main targets are pornography, online gambling, and other sites deemed harmful to society, critics say that often acts as cover for detecting and blocking sensitive political content.
The video site YouTube has been blocked in China since March — apparently because it contained video depicting harsh treatment of Tibetans by Chinese security forces. Twitter and the photo-sharing Flickr service were made inaccessible in June, just ahead of the 20th anniversary of the 1989 military crackdown on pro-democracy demonstrations on Tiananmen Square.
Facebook and Fanfou, a Chinese site similar to Twitter, were cut off after deadly ethnic riots erupted in China's far western region of Xinjiang earlier this month.
"Over the last few months in particular, news (in China) is being circulated through those Twitter-like sites or Facebook-like sites and instantly disseminated on a large scale," said Xiao Qiang, director of the Berkeley China Internet Project at the University of California-Berkeley.
"It makes it very hard for the censors to block the news from circulating ... so they have stopped all these sites I guess while they figure out what to do."
The technology channels of China's leading Web portals, Sina and Netease, could not be opened for several hours after both sites posted news about a Namibian probe into corruption allegations against Nuctech, a Beijing company that makes scanning equipment. The articles were deleted and the channels were online again by late Tuesday afternoon.
Details of the probe had been reported by The Telegraph and The Australian newspapers. Both papers noted that until last year, Nuctech was overseen by President Hu Jintao's son.
The Sina and Netease articles, which were written in Chinese and cited unspecified foreign media reports, made no mention of Hu Haifeng, who is currently the Communist Party Secretary for the holding company that owns Nuctech.
The Telegraph on Monday quoted the director of Namibia's Anti-Corruption Commission, Paulus Noah, as saying Hu was not a suspect in the case.
Screenshots of the deleted Chinese articles have been posted on overseas blogs and circulated via Twitter and e-mail.
A Netease spokesman said the site's technology channel was down due to a technical problem. He refused to give his name or elaborate. A Sina spokeswoman said she was unaware that the portal's technology channel was down. She also refused to give her name or answer additional questions.