China's scientists, artists and entrepreneurs cry foul after Beijing blocked virtual private networks (VPNs) that work around the nation's "Great Firewall" and access foreign websites such as Flickr, Facebook and Google.

Until now, Internet censors had left VPNs alone as a way for millions of China's netizens -- from astronomers to students enlisting in universities abroad -- to have more open Internet access.

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Several VPN companies such as Golden Frog and StrongVPN had complained cyber censors interfered with their services using new, sophisticated methods. A senior Chinese official did acknowledge the government's hand in the VPN service disruptions and warned of more interventions.

Last week, a director of the Ministry of Industry and Information Technology admitted the government was cracking down on VPNs to promote the nation's Internet, adding VPNs were illegal. Ministry official Wen Ku told the People's Daily China needed new ways to deal with emerging problems.

Disabling the country's popular VPNs has angered professors, businessmen and video artists who complain online filtering only ends up hurting the productivity and innovation necessary to breathe new life into China's economy at a time of sluggish growth.

After shutting VPNs, the government cut off from the rest of the world China's astronomers who need updated scientific data overseas; students who need to send online applications to U.S. universities and graphic artists looking for Shutterstock clip art.

Gmail has become useless in China, along with image-sharing websites like Flickr. Forget about staying in touch with Facebook friends.

In the past weeks, a number of Chinese professors vented their frustrations online, especially with blocked access to Google Scholar, a search tool that covers millions of scholarly publications worldwide.

A naval historian, Zhang Qian, compared the situation to living in the Middle Ages in a microblog entry he posted on China's social media site, Sina Weibo.

One biologist pointed out how the frustration with blocked websites was sapping his colleagues' time and energy. For a country that supposedly promotes science and learning, the Internet barriers show hardly any respect for scholars who actually pursue science, he said.

An international news editor of a state-run media outlet, Henry Yang, said he needed to be on top of updates from around the world but couldn't access Facebook to see stories from U.S. broadcasters. Yang said he felt like a frog being slowly boiled in a pot.

Companies with multinational operations are also worried, especially with regulations that force foreign telecom and technology outfits to provide Beijing with "back doors" to their products and to store their data within the country.