By WSJ Staff

From China Journal’s Sky Canaves:

Associated Press

A police officer salutes guests at Zhoushan Oil Reserve in Zhejiang Province, China, Wednesday.

On Tuesday, Chinese users of various U.S.-based Web services – Twitter, Hotmail and Flickr among them – reported a widespread inability to access these services from China. On Wednesday, a number of Chinese sites followed suit, in a manner of speaking.

A series of partial outages and reduced functionality has swept through a large swath of China’s budding social networking corner, according to users and our own spot checks. In some cases, the providers cited scheduled voluntary maintenance. Many Internet users suspect that these moves are a result of heightened sensitivity ahead of tomorrow’s 20th anniversary of the Tiananmen Square crackdown.

Users of China’s most popular homegrown microblogging service, Fanfou.com, reported that the site was down. (On Tuesday it had appeared to be functioning normally). A message on the Fanfou.com home page explains that the site is undergoing server maintenance in order to improve the microblogging experience for its users and expects to be back in service sometime after midnight on June 6. One senior-level Fanfou employee changed his status message on MSN Messenger to read: “Fanfou is now under tech maintenance and will re-open soon. Don’t ask me why.”

Users in China reported that Bing.com, Microsoft’s new search service, was inaccessible from Tuesday, though the mainland China version of Bing, cn.bing.com, was available. That changed Wednesday, when the Chinese-language version stopped working. A spokesperson from Microsoft China said the company did not know the exact reason for the problem and was working to fix it.

Xiaonei.com, a popular Chinese social networking site similar to Facebook, was accessible from Hong Kong, though some users in mainland China reported seeing messages that the site was under maintenance as well. Sources in the company said it was in the process of moving Xiaonei.com’s from Tianjin to Beijing, and that service interruptions could be expected during this period.

When sites become inaccessible to users in China, it’s tough to tell whether they have been purposely blocked by Chinese authorities, if other technical problems are to blame, or if services are blocked just in local areas. Government officials don’t address the blocking of specific Web sites, and when Internet companies take themselves offline, authorities can plausibly say that these are private business decisions that have nothing to do with them.

But Internet users who are keeping tabs on such things note the amazing coincidence of so many sites becoming suddenly unavailable at the same time. The Chinese media blog Danwei posted a link to this Google spreadsheet that lists dozens of sites that are currently either inaccessible or under maintenance. Some of these, such as the knock-off Bullog blog host, have shut themselves down in protest, while others seem to take a tongue-in-cheek attitude toward what’s going on now. A link to Wuqing.org goes to a page that is blank except for one line: “I too am under maintenance!” Dictionary site Wordku.com posted a maintenance notice similar to Fanfou.com’s, but it refers to the period from June 3 to June 5 as “Chinese Internet Maintenance Day.”

Of course, not all sites have been affected. Among many others, Facebook is still accessible, and the microblogging service owned by Tencent, Taotao.com, as well as Tencent’s popular QQ instant messenger, still appeared to be up and running as of Wednesday afternoon.