China's communist authorities have intensified their campaign against the party's biggest potential enemy - the internet - with the recruitment of a growing army of secret web commentators, sophisticated new monitoring software and a warning that all bloggers and bulletin board operators must register with the government or be closed down and fined.

The escalation of the government's effort to neutralise critical online opinion comes after a series of large anti-Japanese, anti-pollution and anti-corruption protests, many of which were organised or publicised using instant messaging services, chatrooms and text messages.

With the number of users forecast to rise above 100 million this year, access to the web is spreading beyond China's well-rewarded middle class and into the more disgruntled factory and farming communities, where young migrant workers are teaching their families about internet cafes.

In response, the propaganda departments of provincial and municipal governments have recently been instructed to build teams of internet commentators, whose job is to guide discussion on public bulletin boards away from politically sensitive topics by posting opinions anonymously or under false names.

Although advertisements are supposed to have been placed in-house, many details about the part-time political pacifiers have emerged in the domestic media. According to the Southern Weekend newspaper, a team of about 20 commentators has been operating in the city of Suqian, in Jiangsu province, since April.

"In the information age and the internet age, the most important and critical mission in front of us is how to seize the initiative on internet opinion and how to seize the high point of internet opinion," the paper quoted the deputy director of the local propaganda department, Zhang Fenglin, as saying.

Applicants for the job - mostly drawn from the propaganda and police departments - were told they had to understand government policies, know political theory, be politically reliable and understand internet technology. Successful candidates have been offered classes in Marxist theory, propaganda techniques and updates on the development of the internet around the world.

A summary of objectives declared that commentators should "be proactive in developing discussion, increase control, accentuate the good, avoid the bad, and use internet debate to our advantage."

Reports that at least two other localities have recruited similar teams suggest the strategy is being encouraged by the central government. Few will admit to the practice, but Nanjing officials said the city was hiring 20 online commentators from the ranks of its existing employees.

"They don't need to give up their current jobs because it is not full time. All they need to do is spend some time every day monitoring internet discussion," said a member of the propaganda department. "There are commentators like this all over the country. Until now we haven't had detailed instructions about how it works. So nothing is clear yet."

Although the existence of an internet police force - estimated at more than 30,000 - has been known for some time, attention has previously focused on their work as censors and monitors. Countless critical comments appear on bulletin boards of major portals such as Sohu and Sina only to be erased minutes, or sometimes just seconds, later. In the most recent case, all postings that blamed corrupt local officials or slow-moving police for the deaths of 88 children in floods last Friday were removed almost as soon as they appeared.

But the task of covertly guiding opinion - as in Suqian - has proved controversial for different reasons. "I think Suqian's practice is not proper," said Zhan Jiang, dean of journalism at China Youth University for Political Sciences. "If officials want to guide public opinion they should publish an editorial in the People's Daily under their own names. It is very wrong to anonymously spread government propaganda. Online commentary is a kind of abuse of power."

China's leading bloggers were equally scathing. "The government's tactics are too funny. They are actually hiring staff to curse online," said Liu Di, who was arrested last year for comments she posted under her internet moniker Iron Mouse. "But it also shows that the government can find no better way to deal with netizens' discussion. Compared to other media in China, the internet is still the most free. It is powerful among young people no matter whether they are chatting online or playing games. It will be difficult for the government to control."