China's best-known microblogging site has introduced new terms and conditions punishing those who post comments deemed offensive, as it comes under government pressure to clamp down on bloggers.

Sina Weibo's new system, introduced this week, will sanction its 300 million users for "spreading false news", "divulging private information" and "launching personal attacks", the company said on its website.

The move to restrict the posting of information deemed sensitive comes amid government jitters over the growing influence of China's weibos -- microblogs similar to Twitter that have taken the country by storm in recent years.

Their popularity is posing a huge challenge to government efforts to control the flow of information in the one-party state, which has the world's largest population of Internet users at more than half a billion.

Beijing regularly blocks Internet searches under a vast online censorship system known as the Great Firewall of China and has placed Sina and its main competitor, Tencent, under pressure to restrict what their users post online.

But the authorities have struggled to control microblog postings -- from information about protests to rumours about political leaders, a particularly sensitive subject in the run-up to a leadership change due later this year.

In March, authorities closed 16 websites and arrested six people for spreading rumours about a military coup in the wake of rising political star Bo Xilai's dismissal as Communist Party head of Chongqing city.

Sina and Tencent were ordered to stop web users from posting any comments for several days after the speculation.

Under the new terms and conditions, Sina Weibo users will each be allocated 80 points, and will have points deducted by the firm each time they post something that contravenes the rules.

If their points fall below 60, they must avoid any further infringements for two months, and if they fall to zero, their accounts will be erased.

In addition, anyone posting "sensitive" information more than five times will have their accounts blocked for 48 hours under the new rules, which have sparked an angry reaction from Sina Weibo's users.

"What they are sensitive to is what people need (to know)," posted one, under the name Jiongxiang.

"Stopping the free flow of people's thoughts will do more damage than stopping the free flow of our rivers," complained another, posting under the name Wang Xiaowen.

Many Internet users in China have used ingenious ways in the past to circumvent the censors -- such as using code words to discuss sensitive subjects.

Some used the Chinese characters for "Shawshank" to refer to the case of the blind lawyer Chen Guangcheng, who recently fled house arrest and is now in the United States.

"The Shawshank Redemption" was a 1994 film about an escape from an American prison.