Access to YouTube.com, usually readily available in China, was blocked after videos appeared on the site Saturday showing foreign news reports about the Lhasa demonstrations, montages of photos, and scenes from Tibet-related protests abroad.
There were no protest scenes posted on China-based video Web sites such as 56.com, youku.com and tudou.com.
The Chinese government has not commented on its move to prevent access to YouTube. Internet users trying to call up the Web site are presented with a blank screen.
Chinese leaders encourage Internet use for education and business but use online filters to block access to material considered subversive or pornographic.
Foreign Web sites run by news organizations and human rights groups are regularly blocked if they carry sensitive information. Operators of China-based online bulletin boards are required to monitor their content and enforce censorship.
China has at least 210 million Internet users, according to the government, and is expected to overtake the United States soon to become the biggest population of Web surfers.
Beijing tightened controls on online video with rules that took effect Jan. 30 and limited video-sharing to state-owned companies.
Regulators backtracked a week later, apparently worried they might disrupt a growing industry, and said private companies that already were operating legally could continue. They said any new competitors will be bound by the more stringent restrictions.