Meanwhile, there are signs that Internet censors' escalating efforts to stifle such calls could cloud the future of some microblogging and social-networking businesses in China.
The statement was posted on the U.S.-based Chinese language news site Boxun, which is blocked in China, and was circulating on Twitter, which is also blocked, meaning that it could probably only be seen by Chinese using proxies or VPNs, virtual private networks, that allow them to circumvent China's web filters.
However, some people reported getting messages about the attempts to organize antigovernment protests via LinkedIn, the business social-networking site, which is not blocked in China and has a Chinese following.
"We invite every participant to stroll, watch or even just pretend to pass by. As long as you are present, the authoritarian government will be shaking with fear," Wednesday's statement said, urging people to turn out in 18 Chinese cities—:five more than were included in the first appeal Sunday.
The statement appears unlikely to generate large protests given how easily Chinese security services neutralized the original appeal Sunday by rounding up dozens of activists, deploying large numbers of police to the planned protests sites, and intensifying censorship of the Internet as well as some text-messaging services.
It does, however, present Chinese authorities with a dilemma: should they ignore the appeal, banking that few people will turn up this Sunday and the idea will soon fizzle out, or should they escalate their efforts—both physical and online—to stamp out even the vaguest possibility that it might attract more widespread support?
China's response after the original appeal was posted on Boxun and spread via Twitter and microblogging sites has illustrated the powerful array of tools at the government's disposal to prevent the kind of uprising that has rocked authoritarian governments across the Middle East and North Africa in the last month. But it is already starting to have broader repercussions, by making Chinese Internet users more aware of the Web controls they are subjected to, highlighting the widespread use of extrajudicial detention, and raising questions about the political risks inherent in some parts of China's Internet industry.
One direct commercial consequence was Deutsche Bank's decision Tuesday to downgrade to "sell" the shares of Sina Corp, the Chinese Internet portal whose microblogging service, Sina Weibo, has become one of the most popular new forums for sensitive political discussion.
"While we continue to recognize Sina's dominance, innovation and leadership in the portal space, and view its Weibo microblog service as a breakthrough in Internet-based communications, we do believe that the risks of tightening government regulation around its "Twitter-like" service continue to mount," Deutsche Bank analyst Alan Hellawell said in a research note.
"We believe the occurrence of [admittedly sparse and lightly attended] demonstrations across China over the weekend may move the authorities to disable aspects of microblog services that they view as destabilizing. Further Mideast unrest could also lead to tightening."
Bill Bishop, a Beijing-based investor who watches the China Internet said that messages about antigovernment protests on LinkedIn could put it at risk of being blocked in China.
"No foreign SNS [social-networking site] is safe," he said.
Hu Jintao, China's president and Communist Party leader, and Zhou Yongkang, its domestic security chief, both made speeches over the weekend calling for tighter supervision of the Internet, even though China already has the world's most sophisticated online censorship machine.
Chinese officials appear to be particularly concerned about microblogs which barely existed just a few years ago, but had 63.11 million users by the end of 2010, according to the latest report from the official China Internet Network Information Center.
Chinese authorities have been making microblogging-service providers block word searches for terms such as "Jasmine Revolution" and "Egypt" to limit the discussion of the recent unrest. Sina Weibo had its entire search function shut down on Sunday.
Wednesday's protest appeal also called for China's Internet users to spread word of the plan using the slogan "lianghui"—which means "two meetings" and is a commonly used shorthand term for the overlapping sessions of China's parliament and its highest consultative body next month.
If the fledgling protest movement co-opts the term, it raises the possibility that Chinese authorities will have to bar searches for a term that Chinese officials are widely using at the moment in state media.
Some delegates to the National People's Congress, as China's parliament is called, have even opened their own accounts on Sina Weibo in order to solicit public opinion on legislative affairs in the run-up to the NPC's opening on March 5.
Meanwhile, China appears to be pressing ahead with its own plans to create new indigenous Internet entities to better exploit and control the virtual world: Tuesday marked the launch of a new search engine by the official Xinhua news agency and China Mobile Ltd., a state-controlled telecom giant.
Panguso.com is the Chinese government's second move into the search-engine market in less than a year; Goso.cn, a news search engine launched by the official People's Daily newspaper, became operational in June last year.
Panguso is similar to Google and the dominant Chinese search engine, Baidu, but appears to have implemented a much higher level of key-word filtering.
For example, a search for "Liu Xiaobo", the jailed Chinese dissident who won last year's Nobel Peace Prize, showed no results, just a message saying "Sorry, no relevant search results were found."
The same search on Baidu came up with 926,000 results, although some of the results could not be seen "in accordance with laws and regulations," according to a message on the site.
Such controls have been highly effective so far in preventing large-scale social unrest from being provoked or organized online.
However, many Internet users are becoming increasingly aware of the extent of the censorship system, as well as how it works, and are either seeking new ways to get around it, or becoming increasingly frustrated at their failure to do so.
One of the most damning critiques of China's censorship system came Tuesday from Murong Xuecun, a popular Chinese Internet author.
"Our mother tongue has been cut into two parts: one safe, and the other risky," he told an audience at the Foreign Correspondents' Club in Hong Kong.
"Some words are revolutionary, and others are reactionary; some words we may use, and others belong to our enemies."