BEIJING (Bloomberg) - China's government has told telecommunications carriers to block individuals' access to virtual private networks by Feb 1, people familiar with the matter said, shutting a major window to the global Internet.

Beijing has ordered state-run telecommunications firms, which include China Mobile, China Unicom and China Telecom, to bar people from using VPNs, services that skirt censorship by routing Web traffic abroad, the people said, asking not to be identified talking about private government directives.

Companies operating on Chinese soil can use leased lines to access the international Web but must register their usage of such services for the record, the people said.

In keeping with President Xi Jinping's "cyber sovereignty" campaign, the government appears to be cracking down on loopholes around the Great Firewall, a system that blocks foreign information sources from Twitter and Facebook to news websites such as the New York Times and others.

While VPNs are widely used by businesses and individuals to access banned websites, the technology operates in a legal gray area.

The Ministry of Industry and Information Technology pledged in January to step up enforcement against unauthorised VPNs, and warned corporations to confine such services to internal use.

At least one popular network operator said it had run afoul of the authorities: GreenVPN notified users it would halt service from July 1 after "receiving a notice from regulatory departments". It didn't elaborate on the notice.

China Mobile, the Hong Kong-listed arm of the country's biggest carrier, declined to comment. Representatives for publicly traded China Telecom and China Unicom (Hong Kong). couldn't immediately comment.

The ministry didn't immediately reply to an e-mail seeking comment.