“It’s creating pressure, and an atmosphere of fear,” said Xie Wen, a veteran of China’s Internet industry who worked as a senior manager for Yahoo! China. “It’s about making people speak less.”

The rising influence of microblogs has been accompanied by the emergence of celebrity users with verified accounts, known as “Big Vs”.

With over 13 million followers, real-estate mogul Pan Shiyi became one of the most celebrated “Big V” bloggers, driving public opinion on pollution by posting details of Beijing’s dirty air levels, which at the time were not officially released.

At a meeting in mid-August, one of China’s top officials responsible for Internet censorship told Pan and other well-known bloggers to be “more positive and constructive” in their online comments, according to the state-run Xinhua news agency.

Pan was later shown in an interview with state broadcaster CCTV, where he appeared contrite and warned of the dangers of “casual” online posts.

Tensions increased with the August arrest of Chinese-American investor Charles Xue, who gathered more than 12 million followers to his microblog with a steady drumbeat of criticism aimed at China’s government, on charges of soliciting prostitutes.

State-media insisted that his arrest has no connection with his online commentary, but government-run broadcaster CCTV showed him in prison clothes while under detention, confessing that he had used microblogging to “gratify my vanity”.

Prior to the crackdown, Chinese microblogs were subject to tight censorship, with posts critical of top Communist leaders or calling for street protests subject to the strictest censorship.

But the latest campaign has led to increased self-censorship, with posts from users with more than 50,000 followers on China’s most popular microblog, Sina Weibo, declining by 20 per cent from January to August, according to figures provided to Dow Jones Newswires.

“The people leading the movement hope that (social critics) will shut up,” Xie said. “A lot of people are changing their topics, talking about light issues and not anything serious.”

Beijing-based Internet analyst Jeremy Goldkorn said: “It’s certainly had a chilling effect, it’s made people nervous.”

Several high-profile microblog users contacted by AFP said they had been avoiding sensitive political topics in recent weeks.

“I feel the pressure, I am more careful about posting about any kind of topic,” said Wang Xiaoshan, a movie actor whose microblog has over one million followers.

“There have always been limits, but now it’s more serious, you could end up in jail,” he added.

Zhou Ze, an outspoken lawyer who has about 160,000 followers, said: “If it’s about serious issues like official corruption, I’ve given up posting, there are more worries.”

“I have more worries about posts relating to officials, especially state-security officials, because it’s them making the arrests,” he added.

The campaign appears to be part of a concerted effort by China’s new leadership under President Xi Jinping to re-assert control over all forms of the media.

Xi last month called on propaganda officials to “build a strong army... to seize the ground of new media”, while China’s press regulator has ordered journalists to undergo “Marxist” training classes, state media reported.

“The Internet is full of negative news of all kinds and critical voices saying the government only does bad things,” a Communist Party journal named Seeking Truth wrote this month in an article calling for stricter online controls.

Alongside celebrities, police nationwide have detained hundreds for posting information online judged to contain “rumours”, according to official reports.

The campaign received a legal boost this month when China’s Supreme court said Internet users could face three years in jail if “slanderous” information spread online is viewed more than 5,000 times or forwarded more than 500 times.

China’s ruling party, which has provided more room for public debate in recent decades, has long been engaged in a cat-and mouse game with Internet users, tightening restrictions in periodic crackdowns, before new forums emerge to challenge such restraints.

Some expect that the recent campaign will fade away like previous ones.

“It’s a short term movement, they won’t have enough space to detain people at this rate,” Ze said.