China's Twitter-like microblogging website Sina Weibo was raucous Thursday with horn-tooting over Beijing's gold rush at the London Olympics, a digital reflection of the nation's exuberant mood — embellished with flashing emoticons.

Earlier passions have been ignited on the site by a deadly high speed rail crash and outrage over factory pollution.

Launched in 2009, China's leading microblog site has given a digital megaphone to more than 300 million Chinese, prompting many to wonder if it might drive Arab Spring-style political change and democratic reforms. Others see the platform as a brilliant new surveillance tool for the communist government in Beijing.

"You get to know what people are saying and ... it's a way for the middle class to let off steam," said Michael Clendenin, managing director of RedTech Advisors, a tech research company in Shanghai.

"It's better to let them blow off steam in a way you can control and delete rather than have 500,000 students all of the sudden show up at your doorstep."

Companies in charge of own censorship

The weibo.com (weibo means microblog in Chinese) site is heavily censored. The site's owner, Sina Corporation, employs around 1,000 people who sift through the digital morass, catching sensitive material that keyword filters miss and deleting it. Not infrequently, they delete whole accounts.

The government requires Sina and other internet companies to do this in-house, and at their own cost, under threat of fines and shutdowns if they fail.

The government, too, has a corps of internet police, believed to be in the tens of thousands, who patrol the web and its total population in China of 485 million. They even boast a mascot, a pair of cartoon police officers named Jingjing and Chacha, a play on the Mandarin word for police.

Sina has domestic competitors that offer their own microblogs, but Sina's service has become synonymous with the Weibo label and has attracted the most high-profile and prolific users. Though modeled on Twitter, Sina's version has more bells and whistles, such as embedded video and images for posts and threaded comments.

Clendenin calls it a "frankenclone."

"It's taken a little bit of Twitter, of Groupon, of Hulu or YouTube and essentially grafted all these pieces together," he said. "In aggregate, it's actually much better than what Twitter is."

Celebrities, cats rule on Weibo

Weibo power users are pop and movie stars. Leading the pack, with more than 22 million fans, is a pillow-lipped beauty with glossy black hair and a passion for refugee causes. No, not Angelina Jolie, but Yao Chen, a 32-year-old actress who frequently tweets about her handsome grey cat, Badun, named after U.S. General George Patton.

Weibo is rife with cat images and banal observations about pets, as well as entertainment gossip, jokes and the ravings of sports fans.

"Chinese athletes, you are so great!!!," Damengmeng Betty posted Thursday on how she felt watching so many of her country's competitors at medal ceremonies. "I feel so excited! Tears fill up my eyes. Can't use words to describe how that feels."

But the service has also given Chinese an unprecedented public platform on which to rage over serious social problems.

When a bullet train crashed last year near coastal Wenzhou, killing 40 people, the fury that erupted on Weibo added to a pressure campaign that saw suspension of construction.

National outrage over graphic photos of a young mother lying beside her dead fetus, which had been forcibly aborted by local officials, sparked a shame campaign and led to punishments in Shaanxi province.

13 per cent of content deleted

The site has been used to organize as well, a rallying point for real-world demonstrations, including rowdy protests against a paper plant last month in Qidong, near Shanghai. It is this utility that makes the Chinese government nervous and that has become the main focus of the censors, according to recent research.

China's online "censorship program is aimed at curtailing collective action by silencing comments that represent, reinforce, or spur social mobilization," said a Harvard study led by social science professor Gary King that was released in June.

The study found that about 13 per cent of China's social media content is routinely scrubbed — up to tens of millions of disappearing tweets per day — but surprisingly, a great deal of negative comments were allowed to slide.

"Posts with negative, even vitriolic, criticism of the state, its leaders, and its policies are not more likely to be censored," King's paper said.

Such criticism may survive because the regime realizes the value of seeing what's on people's minds. Complaints also give the central government in Beijing a relatively unfiltered snapshot of brewing crises in cities and provinces across the country, a huge advantage for top leaders.

"The cat and mouse game is not only the government versus the netizens," said Michael Anti, an internet researcher in Beijing. "You also have a local cat and a central cat ... Weibo more and more is becoming a vehicle for the central government to control the local governments."

Communist Party uses internet to own benefit

Provincial print and broadcast news are routinely censored at the source, while internal government reports are invariably burnished by the cadres preparing them. With Weibo, which is centrally censored by Sina with input from the government, Beijing has a valuable new national monitoring system — one that should make lower-level officials more accountable and prevent them from covering up problems in their backyards.

Jeremy Goldkorn, director of Danwei.com, a firm that researches Chinese media and internet, says Weibo could add "flame to the fire of any kind of anti-government event," but has also become an asset for the ruling Communist Party.

"They've put a lot of energy and effort into understanding the landscape of the internet and how to use it for their own benefit," said Goldkorn. "I don't really see Weibo as causing the next revolution anytime soon."

Even with the weeding out of so much content, Sina Weibo's data tsunami — with more than 100 million messages posted each day — is valuable intelligence to government officials, marketers and any curious China watcher. It offers a more unvarnished and personal glimpse of China than anything you will see on Chinese state-run television or the scrupulously vetted print media.

Citizens winning information war

Users try to fool the censors by posting blocks of text as images so they can't be scanned by automatic keyword searches. They also make liberal use of puns, initials, nicknames and homonyms to dupe the digital knife.

The evasions are hit and miss. Isaac Mao, a popular blogger in Shanghai, had more than 30,000 users when his Weibo account was deleted in June after he made a series of questioning remarks about China's space program.

Mao tweeted that it was "a waste of resources" for China to compete in the space race rather than pursuing less expensive co-operation with other space-faring nations. He said he was "heartbroken" when he found he could no longer log in. Sina's customer service refused to give a reason for booting him off.

He and others, including prominent blogger and social critic Wen Yunchao, have written to investors to urge them to dump Sina stock to express their disgust over its collaboration with government censorship. Meanwhile, the Nasdaq-listed company has struggled to find a way to monetize its hugely popular product.

Still, Mao is bullish on Weibo's potential to help make China a less repressive place. He says it's teaching Chinese how to debate and tolerate diverse opinions while getting them used to the idea that an individual can take part in directing the public agenda. Mao said the platform is eroding the government's grip on public opinion.

"People are starting to know more. They're not stupid like before," Mao said. "The government wins some small battles but they are losing the [information] war."