Access to YouTube in China was denied on Sunday after footage of recent deadly protests in Tibet appeared on the video posting site.
Attempts to call up the site met with a blank screen and an error message saying the web page could not be displayed.
The access problems came after video clips began appearing on the site showing violent unrest in the Tibetan capital Lhasa that triggered a virtual lockdown of the city by security forces.
China, which strictly controls access to information, has kept a tight lid on news out of Lhasa, with foreign journalists being denied access and foreign tourists ordered out of the city.
The only footage broadcast by state-run media so far has been a short clip showing Tibetan rioters in the city destroying Chinese shops, but nothing has been released on the resulting crackdown by police.
China's official death count puts the toll at 10, but the India-based Tibetan government-in-exile says at least 80 deaths have been confirmed.
China also has been regularly blacking out the domestic feed of CNN whenever it runs a story about the Tibet unrest.
Access to popular Chinese-language video posts such as tudou.com were operational on Sunday but a search for videos of the Tibet violence came back with no results.
In late January, China introduced new restrictions on posting online video that critics saw as an extension of the Communist Party's tight noose on the nation's media outlets.
Amid China's information clampdown, the Internet has provided a rare window into the situation, with amateur video and pictures popping up on websites around the world.
© 2008 AFP