Access to popular social networking service Twitter and Microsoft e-mail service Hotmail was blocked across the mainland yesterday afternoon, two days before the 20th anniversary of the Tiananmen Square crackdown.
Indignant users filled chatrooms with protest after Twitter access was denied.
"The whole Twitter community in China has been exploding with it," said Beijing-based technology commentator Kaiser Kuo. "It's just part of life here," he added.
Others said they were unable to access Microsoft's Windows Live and Yahoo's online photograph-sharing service Flickr.
Internet users in Beijing had accessed the services without difficulty earlier yesterday, even with potentially sensitive words such as "Tiananmen."