By Maggie Shiels
Technology reporter, BBC News, Silicon Valley
YouTube is the site that is most often banned or blocked
China's move to block YouTube has been criticised by a leading advocacy group that promotes constitutional liberties in the digital age.
The Centre for Democracy and Technology told the BBC: "China's actions fail to live up to international norms."
The video sharing site has been off limits in China since Monday.
"China's apparent blocking of YouTube is at odds with the rule of law and the right to freedom of expression," said CDT president Leslie Harris.
"Anytime a country limits or takes down content online , it must be forthright and specific about its actions and do so only in narrowly defined circumstances consistent with international human rights and the rule of law," stated Ms Harris.
Google, which owns YouTube, told the BBC that it had no idea why the Chinese government had taken this action.
"We don't know the reason for the block and are working to restore access to users in China as quickly as possible," said spokesperson Scott Rubin.
Earlier in the week, the BBC reported from Beijing that China cut off access to the website because it carried a video showing soldiers beating monks and other Tibetans.
The graphic video was released by Tibetan exiles and showed hundreds of uniformed Chinese troops swarming through a Tibetan monastery. It included footage of a group of troops beating a man with batons.
Tibetans say they have little religious and political freedom under China
In another scene a group of men, including a monk, were beaten, kicked and choked, while they lay on the ground. Some had their hands tied and appeared to be unconscious.
The date and locations of the film have not been confirmed.
Google said it noticed that traffic to China started slowing down on Monday and that by Tuesday morning, it was totally blocked.
When asked about YouTube at a news conference at the beginning of the week, a Chinese government spokesman said: "We encourage the active use of the internet but also manage the internet according to law."
A report published by China's official Xinhua news agency accused the Tibetan government of faking the wounds. No reference was made to YouTube.
"Suppression of speech"
This is not the first time the popular video sharing website has been censored in China.
In 2007, YouTube was blocked during a meeting of the Communist Party Congress in Beijing according to Congressional testimony given last year by Google's deputy counsel Nicole Wong.
At the same time the Dalai Lama was being awarded a Congressional Gold Medal.
"While we were not informed of the exact cause of the suppression of speech and we did not ourselves remove any videos, access to the site in China was reinstated only following the conclusion of the party congress," said Ms Wong.
That incident lasted for 14 days while another incident last year lasted for 6 days and occurred around the same time as this latest one.
China is not alone in prohibiting access to YouTube. Over the years several other countries have done the same thing.
Earlier this month Bangladesh blocked the site for 36 hours after a video was posted showing a tense meeting between the prime minister and angry army officials after a mutiny by border guards in Dhaka that left more than 70 people dead.
The site is presently being blocked in Turkey.
This pointed to a worrying trend said Ms Harris.
"China is not alone in blocking content including YouTube. Online censorship threats are increasing worldwide. YouTube remains blocked for example in Turkey. But China alone refuses to acknowledge or explain its actions."
Paris based Reporters Without Borders also condemned China's action and branded the country an "enemy of the internet" in a report published earlier this month.
The group reported that more than 2,600 websites, blogs, or forums were closed down or blocked around the world in 2007.