Mainland China is becoming a testing ground for online surveillance and censorship, a report by the human rights advocacy group Freedom House said on Thursday.
The report contains preliminary findings from the Washington-based NGO's annual Freedom of the Net report, which is scheduled to be released later this year.
"China increasingly serves as an incubator for sophisticated new types of internet restrictions, providing a model for other authoritarian countries," it said.
Social and political activism has been allowed online in a very limited form, but was manipulated for political gain, the report said. "Sometimes a political faction seemed to briefly lift censorship on content that would discredit an oppenent."
The internet authorities have developed "an extraordinary range of tools to contain critical conversations", it said - possibly affecting the mainland's 591 million internet users, most of whom access the internet on mobiles, according to the China Internet Network Information Centre .
The Freedom House report also pointed out that the growing sophistication of China's cybersurveillance state was driven not by the government, but by internet companies trying to operate in the Chinese market. Censorship and surveillance technology has been developed by service providers trying to stay ahead of the government.
One such change has been a crackdown by internet service providers on virtual private networks, which "tunnel" through China's Great Firewall.
Authorities have also found it easier to regulate cybercafes, which have been increasingly consolidated. Now 40 per cent are owned by chains, the report said.
China most censors cases of collective action, such as strikes and protests, followed by pornography and criticism of censors, according to a Harvard University study published in May.
China's censorship is the "most extensive effort to selectively censor human expression ever implemented", said the study. It is "probably being watched closely by autocrats from around the world," its authors concluded.