A question-and-answer page on Google Hong Kong's website became inaccessible to some mainland Chinese users on Tuesday, underscoring Beijing's sensitivity about the Internet.
The Chinese government, obsessed with maintaining social stability and controlling the flow of information, requires all search engines operating on the mainland to self-censor. It uses a Great Firewall to block overseas sites with content it considers subversive or dangerous.
The Google page (www.google.com.hk/wenda) provides Chinese-speaking Internet users with a forum to ask questions of any description and some visitors had veered into highly sensitive territory.
Several recent questions concerned the June 4, 1989, crackdown on pro-democracy demonstrations around Beijing's Tiananmen Square, a topic banned from public discussion in China.
One questioner asked when China would have its next Tiananmen uprising, with answers including soon; the Communist Party will collapse.
Others included profanities about former leader Mao Zedong or sensitive contemporary issues such as a recent protest to protect the Cantonese language in the southern city of Guangzhou, which ended in scuffles with police.
Multiple users in China reported getting error messages when they tried to access the page.
A Google spokeswoman said there was nothing technically wrong with the site.
If you are noticing there is a blockage you would need to ask the government as it would be an issue at their end, she said.
China's State Council Information Office, one of the country's internet regulators, did not immediately respond to a request for comment.
Google angered Beijing this year by announcing it was no longer willing to comply with censorship rules.
The company closed its local search site and redirected traffic to its site in Hong Kong, a former British territory which returned to Chinese rule in 1997 while retaining a high degree of autonomy.
China has the world's largest Internet market by users at 420 million.
(Reporting by Melanie Lee and Ben Blanchard)