Draft Chinese Internet rules could further restrict access to websites not registered in the closely regulated country, experts said Tuesday, although the measures' potential impact remained unclear.

The proposed rules come as China increases censorship across the board, ratcheting up already strict limits on access to online content and stepping up pressure on the media to toe the government line.

The regulations, released for public comment last week by the Ministry of Industry and Information Technology, aim to update rules for the use of "domain names", the addresses used to navigate the Internet.

The rules are "broad and vague" but in their strictest reading they could be used to "censor any domain name that is not registered in China", said Lokman Tsui, an expert on Internet policy at the Chinese University of Hong Kong.

"Only domain names approved by the authorities are allowed, and other domain names not registered in China now would be under this new regulation de facto blocked".

Violators could be fined up to 30,000 RMB ($4,600).

It was not clear whether the rules would apply to websites hosted outside China but accessible from within the country, or only those located on domestic servers.

But several Chinese news outlets, including the Communist Party-linked Global Times, reported the regulations would probably affect foreign companies, including Microsoft and Apple, which host services on servers in China.

The regulations also stipulate that domain names cannot "endanger state security", "leak state secrets", or "harm national honour".

Kan Kaili, a professor at Beijing University of Posts and Telecommunications, said he believed that the rules were meant to regulate companies in China providing domain registration services, and that they were unlikely to affect access to foreign websites.

Nevertheless, "Chinese authorities are quite cautious about every aspect of the Internet", he said, adding that they "can't lose control over it whatsoever".

China's Great Firewall, the system used to prevent access to select foreign websites such as Google and Facebook, could be rendered "ineffective" without restrictions on domain name registration, he said.

The new rules are open for public comment until April 25. In the past, controversial laws and regulations have undergone significant amendment if they generate heated criticism.

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