Wikipedia's English site is blocked again in China, after over two months of being accessible, continuing a saga of on-again, off-again availability.

Users in Shanghai and Beijing confirmed Wednesday and Thursday that they were no longer able to visit the site. Wikipedia's own account states that the block resumed on Aug. 31, although some users in China said the site has only been unavailable starting this week.

China regularly blocks access to Web sites that it finds objectionable, including those dealing with politically sensitive subjects such as the Falun Gong religious cult and independence for Taiwan and Tibet, along with some pornographic sites. The Chinese government does not announce or comment on when a site is blocked or made available.

Because the version of events or political views expressed on Wikipedia are not necessarily in line with those of the Chinese government, the government may be blocking access to the site.

The current blocking may be related to the upcoming Communist Party Congress, which begins Oct. 15 in Beijing. Held once every five years, the meeting is the Chinese government's most important political gathering, used to create five-year plans, which are the bedrock of China's centrally-planned economy. It is also often used to reshuffle government positions or for leaders to consolidate their power.

While Wikipedia's English site is occasionally available, its Chinese-language sites are almost permanently blocked, although access is sometimes permitted for one or two days at a time.

"Right now there seems to be an intensive government-mandated freeze on the Internet in China, particularly on Web sites with user-generated content," said Jeremy Goldkorn, editor of Danwei.org, a Beijing-based blog that covers China's media. "It seems that the attitude towards Web sites hosted abroad is also hostile right now, which may explain the latest block on Wikipedia."