Google Inc's Gmail was blocked in China after months of disruptions to the world's biggest email service, 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, said 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, who uses a pseudonym.

Google's own Transparency Report, which shows real-time traffic to Google services, displayed a sharp drop-off in traffic to Gmail from China on Friday.

"We've checked and there's nothing wrong on our end," a Singapore-based spokesman for Google said in an email.

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China maintains tight control over the Internet, nipping in the bud any signs of dissent or challenges to the ruling Communist Party's leadership.

The country is host to the world's most sophisticated internet censorship mechanism, known as the Great Firewall of China. Critics say China has stepped up its disruption of foreign online services like Google over the past year to create an Internet cut off from the rest of the world.