Beijing: China has ramped up its online censorship efforts, with LinkedIn, a social networking site for professionals, the latest site to be blocked as authorities apparently move to snuff out efforts to organise anti-government protests.

Attempts from Beijing to reach the LinkedIn website failed Friday, with the internet browser displaying an error message. Some LinkedIn users said the blocking of the website began Thursday.

Social networking sites were used by activists in north African and Middle Eastern countries to organise anti-government demonstrations which eventually toppled leaders in Egypt and Tunisia. The movements have been dubbed the "jasmine revolutions".

Inspired by those popular uprisings, anonymous internet users have called for anti-government gatherings every Sunday in over a dozen Chinese cities. In Beijing Sunday, the first gathering seemingly attracted more police and foreign journalists than protesters.

The Chinese government runs a pervasive internet censorship system that blocks content that undermines the ruling Communist Party's grip on power.

Searches for the term "jasmine" on Chinese microblog service Sina Weibo and Facebook-clone Renren produced no results Friday. The Chinese name of US Ambassador to China Jon Huntsman, too, appeared to have been censored on Sina Weibo.

Authorities fear activists could use foreign social networking sites like LinkedIn, Facebook and Twitter to organise anti-government protests, and so they block access to the sites.

Chinese alternatives to these sites are popular in China. But Chinese internet companies quickly delete posts that could undermine Communist Party rule.

In addition to tightening its internet controls, authorities harassed and detained scores of activists and human rights lawyers in the days before the first planned protest. Human rights groups have widely condemned the crackdown.