Mainland internet users can no longer access slideshare.net, a website where about 29 million people from around the world upload and share PowerPoint presentations and other types of documents. Mainland users who tried to get onto the site got an error message. Access to the website from Hong Kong remained normal. It is not clear why the site has been blocked. Most content on the website's front page yesterday was not political, and none of it was directly related to China. Featured slideshows included a crash course on mathematics, a student's resume and criticism of the US health-care system. The site does have material that would be banned on the mainland. The first presentation that pops up after searching for Tibet is titled 'Stop the cultural genocide in Tibet'. But that content was submitted four years ago. The last major website blocked by the central government was Bloomberg.com, after the news agency published a story last month about the immense wealth of members of Vice-President Xi Jinping's family. Slideshare.net did not respond to inquiries yesterday, but some information-technology experts said that they were not surprised. Jason Ng, the founder of kenengba.com, a popular IT blog on the mainland, said yesterday that sooner or later all overseas websites that met three criteria would be blocked by the central government's 'Great Firewall'. The websites at risk were 'those that allow users to freely upload content without censorship, that have built up a large user base in China and that have prompted many copycats'. Examples included YouTube, Facebook and Twitter, he said.