China has detained at least 33 people since the commericalisation of the internet there in 1995, according to new report by Amnesty International.
In one case, the report says, a former police officer was sentenced to 11 years for downloading articles from Chinese democracy sites based outside China.
The report - entitled People's Republic of China: State Control of the Internet in China- said the detainees include political activists and writers to members of unofficial organizations, including the Falun Gong spiritual movement.
Amnesty has called on the Chinese authorities to release all those currently detained or jailed for using the Internet to peacefully express their views or share information.
"Everyone detained purely for peacefully publishing their views or other information on the Internet or for accessing certain websites are prisoners of conscience ... should be released immediately and unconditionally," Amnesty International said.
Their report also alleges that two of those detained for Internet-related offences have died in custody, apparently as a result of torture or ill-treatment at the hands of the police.
Both are members of the Falun Gong spiritual movement, which was banned as a "heretical organisation" in July 1999.
"As the Internet industry continues to expand in China, the government continues to tighten controls on on-line information," the report adds."These have included the filtering or blocking of some foreign websites, the creation of special Internet police, the blocking of search engines and actions to shut down websites which post information on corruption or articles critical of government."In August China blocked access to the Google Internet search engine for a brief period, diverting users to local Chinese search engines instead.
In recent weeks, Beijing shifted tactics again, opening up some previously blocked Web sites, but making it impossible for users to open documents on those sites that relate to China.
The Ministry of State Security has reportedly installed tracking devices on Internet service providers to monitor individual email accounts and all Internet cafes are required to register and inform the police about their customers.
Authorities have also forced Internet companies to take greater responsibility for policing the web. A "Public Pledge on Self-Discipline" was introduced in August 2002 under which signatories agree not to post "pernicious" information that may "jeopardise state security, disrupt social stability, contravene laws and spread superstition and obscenity".
In June 2002 the number of Internet users in China had reached almost 46 million and experts believe that within the next four years China is likely to become the largest Internet market in the world.
Since 1995 more than 60 rules and regulations have been introduced covering the use of the Internet.