China has introduced new rules to gag its increasingly vocal netizens, threatening bloggers and simple social media users with up to three years in jail for posting what Beijing describes as damaging false rumours.

China's top court and prosecutor have stipulated in a judicial interpretation that a libellous online message could land its poster behind bars if it is widely circulated on the internet.

If the post is viewed by at least 5,000 users or reposted more than 500 times, the author is to be charged with defamation, which carries a standard sentence of three years in jail.

Prison doors will also open when authorities deem the spreading of misinformation as a "serious case", regardless of the number of readers.

Serious cases include posts that damage the nation's image or "cause a bad international effect" as well as messages leading to mass protests or instigating ethnic or religious clashes.

False posts found to cause mental illness, self-harm or suicide are also to be considered as such, the document jointly issued by the Supreme People's Court and Supreme People's Procuratorate states.

"People have been hurt and reaction in society has been strong, demanding with one voice serious punishment by the law for criminal activities like using the internet to spread rumours and defame people," said the court spokesman Sun Jungong.

"No country would consider the slander of other people as 'freedom of speech'."

An increasing number of cases of corruption and abuse of power by party officials and security forces have been exposed by Chinese bloggers, forcing authorities to take action.

The censorship-prone Communist Party has been trying to stem the social media tide by launching a police crackdown on journalists and bloggers accused of spreading false rumours.

Sun said the new rules are not meant to discourage Chinese internet users in exposing corruption and other violations, as no charges will be filed if the information has not been fabricated to slander others.

However critics will simply allow corruption to flourish, free from the bounds of accountability.

"This gives every corrupt local official a convenient tool to arrest anyone who criticises him," Michael Anti, a prominent blogger and media commentator in Beijing told The Guardian. "It means the end of the online anti-corruption movement."

"I would have to shut up on the internet now," a Chinese user told South China Morning Post. "If you want to put a person in jail, the easiest way would be to forward his untrue post 500 times."