Networking site falls victim as government stifles online calls for a pro-democracy uprising in wake of Middle East upheaval

LinkedIn has become the latest major social network to fall victim to China's renewed crackdown on the internet, as the ruling Communist party stifles online calls for a pro-democracy uprising.

The networking site for business professionals – which has more than 1 million users in China – was blocked for the first time in the country on Thursday. Internet searches on the Chinese Twitter equivalent are also being heavily censored.

Authorities have tightened control of the internet in recent days in the wake of the political uprising sweeping the Middle East. Activists have described the situation as "one of the worst crackdowns on the mainland's activists in recent years".

Hani Durzy, a spokesman for LinkedIn, said on Friday: "We can confirm that access to LinkedIn is being blocked for some in China.

"This appears to be part of a broader effort in China going on right now, involving other sites as well."

LinkedIn has been allowed to grow largely unhindered in China, unlike more popular Western social networks such as Twitter, Facebookand YouTube which remain blocked.

A LinkedIn user named Jasmine Z set up a "Jasmine Voice" discussion group on the network on Wednesday, claiming to be "becoming a critical dissent dying for democracy, freedom and justice in my homeland".

Authorities have also blocked searches for the Chinese name of the US ambassador, Jon Huntsman, after a video was published of him near a pro-democracy gathering in Beijing.

Searches for "Egypt", "jasmine", "jasmine revolution" and "Hillary Clinton" were also censored on the popular Chinese internet portal Sina.com.

A number of activists have been arrested in the country over the past week, charged with "endangering state security" as fresh calls for demonstrations were posted on the overseas website Boxun.

China's tight grip on the internet is thought to involve one of the world's most sophisticated online censorship systems.

But the creator of "The Great Firewall", Dr Fang Binxing, recently admitted that it could be subverted by using technology called virtual private networks (VPNs). "So far, the GFW [Great Firewall] is lagging behind and still needs improvement," he told a Chinese newspaper.