When a huge mudslide swamped a Chinese town in August, killing at least 1,500 people, word first reached the world thanks to a digital camera-wielding, 19-year-old micro-blogger who idolises Lady Gaga.

Wang Kai's reports on a Chinese Twitter-like service from the northwestern town of Zhouqu made him an online celebrity and underlined the potential impact of the fast-growing new medium in the world's largest online population.

Things looked grim last year when China's censors added Twitter to their list of blocked foreign services amid government accusations that social media were used to fan deadly ethnic unrest in northwestern China in July 2009.

But several Chinese clones soon sprung up, offering users a platform for sending 140-character messages via provider websites or mobile phones -- while exercising heavy self-censorship to keep authorities happy.

China's 420-million web users have seized on micro-blogging as a new avenue for mass expression in a tightly-controlled information landscape.

From almost nothing last year, there are an estimated tens of millions of micro-blogging, or "weibo", accounts in China. Active users will hit 65 million by year's end, the Data Center for the Chinese Internet (DCCI) predicts.

"Weibo's role is huge," Wang Kai, now an English student at university, told AFP when asked to explain its appeal.

"It provides you with your own platform for sending out really meaningful microblogs and opinions. I hope it can be used to help people solve problems."

Users say China's half-dozen providers offer services that are superior to those of Twitter, such as embedding of videos and photos.

They add that more can be expressed in 140 of the Chinese language's pictographic characters than in English.

But the real impact of "weibo" could lie in its ability to knit together -- through the rapid, mass sharing of links -- the countless Chinese blogs, forums and other websites that are the dominant outlet for public expression.

"The density of information they have created, their frequency of dissemination and the degree of connectivity they have enabled for web users far surpass any previous form of Internet use," Hu Yong, an author of several books on the Chinese Internet, wrote in a recent opinion piece.

The DCCI predicts active user accounts will exceed 400 million within three years as China's online population grows. Twitter said in early September it had 145 million users.

A recent poll found that about 90 percent of under-40s use a "weibo" service, engaging in lively discussions on entertainment, lifestyle, the job market or flogging a company's products.

But several cases also have highlighted its potential for rattling the government, which aggressively censors web content it views as a political threat.

In July, an investigative reporter who exposed alleged graft by a listed company in eastern China found himself on a most-wanted list for slander.

Qiu Ziming of the respected Economic Observer financial weekly went on the run, drawing thousands of "followers" with defiant blog posts declaring his innocence and alleging a cover-up.

Police eventually quashed his arrest order after public pressure in an episode that triggered a debate about abuse of official power.

Rumours of a split between President Hu Jintao and Premier Wen Jiabao were a hot recent topic after Wen made comments seen as urging political reform, and chatter on numerous graft cases and other scandals was widely credited with adding to online pressure that resulted in government action.

Micro-blogging services were briefly cut in July in what analysts said was a message from the government to users to toe the line, but authorities are beginning to use micro-blogging for their own ends as well.

A June government white paper on the Internet singled out micro-blogging as a useful communication tool and praised Internet users for "supervising" the government.

Local-level government agencies nationwide, such as Beijing's police, have set up accounts in a bid for openness -- or at least to guide public sentiment.

"The Chinese government learns very quickly and is very much at the forefront or ahead of the curve of what is on the Internet," said Bill Bishop, co-founder of the news site MarketWatch.com, who now blogs about the Internet in China.

"They are working very hard to effectively channel and manage public opinion. Weibo offer unprecedented challenges and opportunities for the government PR folks to deal with issues in near-real time."

Few experts however see microblogs as posing any imminent threat to the Communist government.

Beijing keeps firm control by restricting weibo services to top Chinese Internet firms well-versed at self-censorship, said Jeremy Goldkorn, editor of the China media website Danwei.org.

"(Micro-blogging) adds to the pressure but it's not enough of a revolution to rewrite the rules of the game. The government can just hire more censors," he said.