WASHINGTON (AFP) - China has expanded its Internet censorship efforts beyond its borders with a new strategy that attacks websites across the globe, researchers said on Friday.

The new strategy, dubbed "Great Cannon," seeks to shut down websites and services aimed at helping the Chinese circumvent the "Great Firewall," according to a report by the Citizen Lab at the University of Toronto.

"While the attack infrastructure is co-located with the Great Firewall, the attack was carried out by a separate offensive system, with different capabilities and design, that we term the 'Great Cannon,'" the report said.

"The Great Cannon is not simply an extension of the Great Firewall, but a distinct attack tool that hijacks traffic to (or presumably from) individual IP addresses."

The report supports claims by the activist organisation GreatFire, which last month claimed China was seeking to shut down its websites that offer "mirrored" content from blocked websites like those of the New York Times and others.

The technique involves hijacking Internet traffic to the big Chinese search engine Baidu and using that in "denial of service" attacks which flood a website in an effort to knock it offline.

The Citizen Lab researchers said they found "compelling evidence that the Chinese government operates the GC (Great Cannon)," despite Beijing's denials of involvement in cyberattacks.

Because the Great Cannon is located in proximity of the Great Firewall, this "strongly suggests a governmental actor," said the report, which included collaboration from researchers at the University of California and Princeton University.

The researchers said that deploying the Great Cannon "is a major shift in tactics," and that it would likely "require the approval of high-level authorities within the Chinese government." "The government's reasoning for deploying the GC here is unclear, but it may wish to confront the threat presented to the Communist Party of China's ideological control by the 'collateral freedom' strategy advanced by GreatFire.org and others," the report said.