A collaborative experiment with the community translation website Yeeyan to publish a selection of Guardian stories in Mandarin has been closed down by the Chinese authorities.
Yeeyan's main website, which also publishes other material translated by its members, has also been shut down. No reason has been given. The Guardian is seeking an explanation from the Chinese government about why the site was shut, and when it will be allowed to resume publication.
Alan Rusbridger, editor in chief of Guardian News & Media, said: "This is a very disconcerting development. Yeeyan is a wonderful community of mostly volunteer translators who give Chinese web users access to a wide range of content published outside China, including Guardian reporting and commentary.
"We hope this move does not represent an attempt to suppress independent-minded journalism, and that the Chinese authorities can reassure us that Yeeyan and the Guardian will be allowed to resume publication."
Yeeyan is the largest open translation community in China. As of June this year, it had more than 90,000 registered users, including about 5,000 community translators who have published nearly 30,000 translations on the site.
China has more than 300 million internet users and employs some of the world's tightest controls over what they see. The Chinese government's official line is that there is no censorship in China. But it has huge numbers of internet monitors who watch over the web, blacklisting websites and filtering out sensitive content. The country is often criticised for having the so-called Great Firewall of China, a censorship programme that strips the internet of political dissent.
After a temporary easing up during the 2008 Olympics, Chinese censors have blocked access to several popular online services this year. Facebook, Twitter, Hotmail and the photo sharing service Flickr were shut down in July, two days before the 20th anniversary of the crackdown on democracy protests in Tiananmen Square. It is believed China's decision to block social networking sites followed the use of them by Iranian demonstrators to publicise the crackdown after that country's contested presidential election in June.
Media commentators believe the crackdown this year is linked to a number of "sensitive" anniversaries, including the 4 May student uprisings of 1919, the 1959 Tibetan uprising, Tiananmen Square, and the 60th anniversary of the founding of the People's Republic of China.
US president Barack Obama criticised China's firewall in a speech during his first official visit to the country last month.
"I'm a big supporter of non-censorship," Obama said. "I recognise that different countries have different traditions. I can tell you that in the United States, the fact that we have free internet – or unrestricted internet access – is a source of strength and I think should be encouraged."