The Google-owned video sharing site is believed to have been cut off due to footage of government law enforcement beating monks and other citizens of Tibet, according to the BBC.
China's crackdown on "indecent" websites has also been seen an effort to squash political dissent.
It's still not known where the footage was actually shot or when, though Beijing claims it did not take inappropriate actions in dealing with Tibetan protests.
The BBC reports a Foreign Ministry spokesman said Tuesday China "is not afraid of the Internet," but would not confirm the blocking of YouTube.
Google noticed a drop in Chinese Web traffic on Monday and Chinese surfers kept receiving "network timeout" messages, according to TGDaily.
YouTube has also been banned in nations that include Bangladesh, Thailand, Pakistan and Turkey because of political content. China has blocked YouTube before, cutting off the site in March 2008 during Tibetan riots. Even sites such as the New York Times and Voice of America have been blocked or censored, as well as BBC and CNN television broadcasts.
Free-speech groups have spoken out in force, reports ZDNet.
"China's actions fail to live up to international norms. China's apparent blocking of YouTube is at odds with the rule of law and the right to freedom of expression," said Leslie Harris, president of the Center for Democracy and Technology. "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."
In a statement, the Global Network Initiative said, "Freedom of opinion and expression is a human right and guarantor of human dignity. The right to freedom of opinion and expression includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers."
Also taking China to task was the Committee to Protect Journalists, saying it was "deeply concerned." The organization's Deputy Director Robert Mahoney called the YouTube blocking "a sign of escalating restrictions on media freedom. Authorities must explain why YouTube is inaccessible."
Google spokesperson Scott Rubin would not address possible reasons for the cut-off, only stating the service was "working to restore access to users in China as quickly as possible."