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Google was working late Sunday night to restore its YouTube video service in China, after the Chinese government blocked access to the site, which was flooded with videos of clashes between police and protesters in Tibet and other cities.

The search advertising giant said it was investigating "reports of users being unable to access YouTube" in China, and trying to get the site back online.

"We are looking into the matter, and working to ensure that the service is restored as soon as possible," a spokesperson for YouTube, which is owned Google, told Portfolio.com by email.

Attempts to load YouTube in China — which has 210 million Internet users — were met with a blank screen over the weekend.

China has long been criticized for its campaign to control the Internet in China — dubbed "The Great Firewall," which some consider to be an unfair restraint of trade.

Google declined to specifically say what it was doing to restore service. And athough it has some politically powerful allies, including former vice-president Al Gore, a company adviser, and presidential hopeful Barack Obama, it is unclear how much influence it has with the Chinese government.

Indeed, Google's effort to restore YouTube in China — even as the government blocks the site — puts the company at odds with a regime it has been accused of deferring to in order to penetrate the Chinese market.

Google has been harshly criticized for its decision to offer a government censored search engine in China which omits information the government does not want disseminated. Western Google users can find many pictures of the Tiananmen Square protest that Google users in China cannot, for example.

Google has argued that "some Google" is better than "no Google," which could be the case if the company did not agree to the government's censorship policy.

Some Chinese-language video websites such as 56.com, youku.com and tudou.com remained available but news agencies were unable to find any videos of the Tibet violence.

Chinese authorities also reportedly blocked domestic feeds of CNN and BBC when news reports of the violence were broadcast.

China's efforts to censor video coming out of Tibet is reminiscent of the situation in Myanmar (formerly Burma) last year, when the ruling junta shut down the country's internet access to censor information about its crackdown on Buddhist monks who had taken to the streets.

Ian Bremmer, president of Eurasia Group, a geopolitical forecasting firm, said that authoritarian regimes are learning to crack down on dissent on the Internet.

"Especially in times of crisis, where social dissent can threaten the very existence of the government, authoritarian regimes want to keep potential opposition isolated and incommunicado," Bremmer told Portfolio.com by email. "That typically means media blackouts, and especially the internet."

Bremmer said China must weigh the potential consequences of its crackdown in Tibet on international public opinion, especially as it prepares to host the 2008 Olympics this summer.

"China has risked quite a bit by holding the Olympics, where a favorable public opinion is critical," Bremmer said. "I suspect there are no few Chinese policymakers that would rethink that decision at this point."

by Sam Gustin