When Chinese journalist Wang Keqin found himself cornered in the countryside two years ago by police who were trying to stop him looking into a rape case involving local officials, he looked online for help.
Wang, one of China's most dogged investigative journalists, and his colleagues called a friend who posted constant updates about their stand-off with encroaching police to a Twitter-like microblog site. Authorities in Badong County, central China, were soon flooded with phone calls from citizens warning them not to detain or hurt him.
"The county public security bureau was overwhelmed by all the calls. It was like a wave of pressure. Weibo saved me that time, and I've also used it to save people being chased by officials," he said, using the Chinese term, "Weibo", for the microblogging services that have bloomed as platforms for sharing news, views, gossip and public outrage.
"For Chinese people, Weibo is creating an arena that is much more free than traditional media," said Wang, who is well known for his painstaking reports on corruption and official misdeeds.
"It's also turning more Chinese people into citizen journalists," he said. "Weibo is already a massive force. It can't be shut down, although they might try to shut down VIP users," he added, referring to online activists.
China's microblog sites, which claim 195 million users and allow people to shoot out short bursts of often strongly worded opinion, have put China's Communist rulers in a difficult spot. Fearing an uproar if they block the sites outright, the censors struggle to keep ahead of the rapid-fire messages that often spread news and opinion the government would like to contain.
Chinese officials, Internet operators, media and citizens are all players in an online contest over how far microblogs will be allowed to challenge the censorship demanded by the Communist Party.
Twitter itself is blocked in China, along with Facebook and other websites that are popular abroad.
"Microblogs have pushed more of the traditional media to become more liberal and challenging," said Wang Junxiu, a Beijing Internet entrepreneur and commentator who closely follows the microblogging world.
"They've also seen the role that social media played in the Middle East," he added, referring to the popular uprisings across the Arab world that rattled Chinese leaders.
"But under current conditions the government could not shut down microblogging. There are 200 million users, remember."
China's microbloggers have shown their collective potency in a string of recent official scandals, particularly the online uproar in the wake of a high-speed bullet train crash last month in which 40 people died.
These scandals have followed the same arc – of official censorship, spin and stonewalling buckling under the weight of rowdy microblog users impatient with the slowness and fetters of traditional media.
"People online seize on anything about officials and corruption, and they don't let up," said Liu Zhengrong, an official at the State Council Information Office who oversees Internet controls said, according to a Chinese newspaper, the Xi'an Daily.
"On the Internet, the public can send out something from multiple points and then to other multiple points," Liu added, referring to microblogs. "Very quickly, the whole world knows."
"Leading officials must not underestimate the intelligence of the public," he added.
State-controlled media coverage of the train crash at first followed a familiar script, faulting nature and foreign technology, and throwing a spotlight on heroic rescue efforts.
Within days, however, that script began to collapse as scepticism and outrage spread quickly in microblog traffic, fanning public ire and emboldening journalists. Newspapers and magazines were soon spurning censors' directives to stick to positive news and began excoriating the railway ministry.
"Especially in times of disaster, such as the high-speed railway disaster, microblogs spread news to journalists who can be on the scene even before the central Propaganda Department sends out a ban [on reporting]", said the editor of one popular Chinese newspaper. He spoke on condition of anonymity, citing possible punishment for discussing government policies.
"Microblogs provide some additional protection, because it means that once a story breaks, everyone pitches in with information, not just official journalists, so enforcing a ban on news becomes much harder," he said.
"It magnifies the impact of media reports, but it also means that no one newspaper or reporter stands out as a target."
Nobody expects China's censorship to crumble. Indeed, by late July China's propaganda machinery had reasserted itself, forcing newspapers to cancel critical stories and magazines to pull issues off the newsstands. But shutting down microblogs does not appear to be an option.
"We see the tensions between the government officials and the public in China acting out on a daily basis on Sina Weibo, and there's just an assumption that whatever the government says it can't be true," said David Bandurski of the China Media Project at the University of Hong Kong, who studies Chinese news media and censorship.
"Social media are going to be an issue, particularly after what we've seen this year. The question is how exactly they're going to tackle it," he said of the government's response.
That question looms over Sina, the operator of China's most popular Weibo site by far with 140 million registered users.
Microblogging, the hottest social networking product to hit China's Internet scene in years, is the reason for Sina's record high stock price this year and the "buy" rating 13 analysts have on the company.
By the end of June this year, the number of Chinese using microblogs had shot up by 209 per cent on late 2010 levels, according to China's official Internet information agency.
But with Internet users able to use that platform to spread news of problems such as lead poisoning outbreaks before local officials can react, operators such as Sina struggle to balance the expectations of both citizens and state censors.
"The trick for Sina will always be keeping the platform lively enough and genuine enough so that it remains relevant, while also keeping it tame enough to satisfy any government concerns", said Michael Clendenin, managing director of tech consultancy RedTech Advisors.
"You have to remember that the majority of Weibo users are young and highly educated – not the types to be easily duped by ham-handed propaganda," Clendenin said.
This week, Weibo users were complaining that their messages about the July 23 train crash were being "harmonized", a euphemism netizens use to describe censorship and removal of their postings.
Sina's chief executive Charles Chao is a U.S.-educated former journalist. In an interview with CNN earlier this month, Chao admitted that censorship was a part of daily operations on Weibo but defended the platform, saying it has enabled greater freedom of expression.
"Weibo actually brings that freedom to the next level so not only can they express, they can also distribute their content and opinions with their Weibo account," Chao said, according to a transcript of the interview.
Some of the self-censorship measures taken by Sina's Weibo and other Chinese microblogging sites include taking down politically sensitive posts, blocking the search of certain keywords and preventing posts that contain those keywords.
Those steps have drawn catcalls from users, as have recent comments on state television scolding microbloggers for spreading "rumours". But even supporters of tightened controls on microblogs said shutting down the sites would risk sparking much worse public outrage.
"Now everyone – users, the government, site operators – are wondering about how to manage the microblogging sphere that's developed so quickly," said Dou Hanzhang, a Beijing-based researcher who has helped form a "Rumor Quashing Alliance" on Sina's Weibo site.
"If the government shut down Weibo, that would trigger outrage and show that the government lacks the competence to manage it," he said.