A fire at a Beijing cyber cafe this month that killed 24 young people is being used as a pretext for the clampdown, the Hong Kong-based Information Centre for Human Rights and Democracy said.
China has long expressed concerned about "unhealthy" web content, and curbs access to many sites showing pornography, politically subversive material, foreign news or information on spiritual and religious groups such as the banned Falungong movement.
For some time, filtering software has been installed at prominent Internet cafes in major urban centres like Beijing, Guangzhou and Shanghai, but according to the Information Centre, this is now spreading throughout China.
Software like the "Filter King" programme not only record the number of times surfers try to access banned sites, but can also send daily reports to local police Internet units.
According an advertisement on the website of Filter King manufacturer Zetronic, their system is capable of gathering information on half a million items of "unhealthy information".
If cafes register their customers, this allows police to find out the identities of those who have accessed banned sites, it said.
Internet cafes have mushroomed across China in recent years as customers, predominantly young people, flocked to take advantage of cheap access to computers, mainly for e-mail, web chats and games.
However the cafes have also helped spread information through the country, for example via occasionally outspoken on-line discussion forums.
Provisional figures show that by the end of March the country also had an astonishing 200,000 Internet cafes, only a fraction of which were officially licensed.
Unregistered outlets have multiplied due to increasingly stringent government rules on cyber cafes and Internet usage, cafe operators have said.
According to official figures, the country had 33.7 million Internet users at the end of 2001, an increase of 49.8 percent from the year before.
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