China has fortified its Great Firewall with a crackdown that will make it harder to access the dozens of overseas websites that are banned in the country, such as Facebook and Twitter.

The “cleaning up” operation, which would make it more difficult for some foreign businesses to operate websites in China, was announced after Xi Jinping, the Chinese president, spoke of Beijing's desire for increased globalisation at the Davos forum last week.

Authorities are rolling out a 14-month crackdown targeting China-based providers of virtual private networks (VPNs), which help people access popular sites such as Facebook, Twitter and Youtube. The websites are blocked on the Chinese mainland.

The new rules, which force domestic VPN providers to register with regulators, come after a series of crackdowns on the Chinese Internet which observers see as part of wider assault on freedom of speech.

Many expats living in China are expected to be largely unaffected by the new rules, as they use VPN providers which are based overseas.

While domestic Internet providers appear to be the main target for authorities, few specifics are contained in the official notice from the Ministry of Industry and Information Technology .

Chinese ‘security’ laws are often couched in vague terms in order to give ample room on interpretation.