The Chinese government has announced plans to police web forums, chat rooms and blogs alongside other websites.
Websites in China have long been required to be officially registered.
The authorities are now determined that blogs should also be brought under state control.
Press advocacy group Reporters without Borders said the initiative would "enable those in power to control online news and information much more effectively".
Private bloggers must register the full identity of the person responsible for the sites, the Chinese Ministry of Information Industry (MII) said.
Commercial publishers and advertisers can face fines of up to one million yuan (£66,000) if they fail to register.
All blogs and websites must be registered by 30 June.
"The internet has profited many people but it also has brought many problems, such as sex, violence and feudal superstitions and other harmful information that has seriously poisoned people's spirits," said a statement on the MII website, explaining why the new rules were necessary.
It has developed a system which will monitor sites in real time and search each web address for its registration number. Any that are not registered will be reported back to the Ministry, the statement said.
Blogs are often used in countries where freedom of speech is limited as a way of speaking out against the ruling power.
The new rules could be devastating for bloggers who do not toe the Chinese Communist party line, said Reporters Without Borders.
"Those who continue to publish under their real names on sites hosted in China will either have to avoid political subjects or just relay the Communist Party's propaganda," the organisation said.
"The authorities hope to push the most outspoken online sites to migrate abroad where they will become inaccessible to those inside China because of the Chinese filtering systems," it added.
Known as the Great Firewall, the filtering system used by the Chinese government is not entirely unbreachable; for every new restriction and technical door that it slams shut, the Chinese people find a hack, a workaround or an entirely new way of communicating.
According to official figures, about 75% of sites have already complied with the new procedure.
In May, many bloggers received e-mails telling them to register or face having their blogs declared illegal.
But one anonymous China-based blogger told Reporters Without Borders that when he phoned the MII to register he was told not to bother because "there was no chance of an independent blog getting permission to publish".
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