Dissident artist Ai Weiwei warned the Chinese government that its attempts to censor the internet would inevitably fail, in an article published in Monday's Guardian newspaper.

Ai, who was held for 81 days last year as police rounded up dissidents amid online calls for Arab-style protests in China, wrote in the British newspaper that new "real identity" rules to curb troublesome microbloggers would only "push the problem to the next generation".

"In the long run, they (the government) must understand it's not possible for them to control the internet unless they shut it off - and they can't live with the consequences of that," he wrote.

"The people will always have the last word - even if someone has a very weak, quiet voice. Such power will collapse because of a whisper.

"The internet is uncontrollable. And if the internet is uncontrollable, freedom will win. It's as simple as that," he added.

Separately, Google co-founder Sergey Brin told the paper that online freedom was under severe threat from governments and giant internet firms like Facebook.

"I am more worried than I have been in the past," he said. "It's scary."

He cited "powerful forces", including countries eager to control the communication channels of their citizens, the entertainment industry's keenness to stamp out piracy and the software constraints imposed by firms such as Facebook and Apple.

The 38-year-old billionaire, who was reported to be behind Google's partial withdrawal from China in 2010, disagreed with Ai's belief that China would have to loosen its censorship laws.

"I thought there was no way to put the genie back in the bottle, but now it seems in certain areas the genie has been put back in the bottle," he told the Guardian.

Brin also claimed that Google would not have survived in today's climate due to the control that Facebook, which is due for a mammoth stock market flotation, exerts over the internet.