Google's Gmail service was blocked in China, with an anti-censorship advocate suggesting the Great Firewall was to blame. Large numbers of Gmail web addresses were cut off in China on Friday, according to the GreatFire.org, a China-based freedom of speech advocacy group. Users said the service was still down on Monday.

"I think the government is just trying to further eliminate Google's presence in China and even weaken its market overseas," said a member of GreatFire.org.

"Imagine if Gmail users might not get through to Chinese clients. Many people outside China might be forced to switch away from Gmail."

Google's own Transparency Report displayed a sharp drop-off in traffic to Gmail from China on Friday.

China uses the world's most sophisticated internet censorship mechanism, known as the Great Firewall of China.