British Foreign Secretary William Hague issued a warning Tuesday to countries that try to restrict Internet freedom as he opened a global conference designed to set up "rules of the road" for cyberspace.

Government officials, tech firms, NGOs, bloggers and security experts from more than 60 countries are at the two-day talks in London, although the main speaker, US Secretary of State Hillary Clinton, pulled out at the last minute.

In his opening speech to delegates including officials from Russia and China, Hague said the social and economic benefits of the Internet were immense and warned that any states that sought to block online activity would lose out.

"We must aspire to a future for cyberspace which is not stifled by government control or censorship, but where innovation and competition flourish and investment and enterprise are rewarded," the foreign secretary said.

Hague warned that human rights, particularly the right to privacy and freedom of expression, "should carry full force online".

"We reject the view that government suppression of the Internet, phone networks and social media at times of unrest is acceptable," he said.

Although he was likely referring to the Middle East and North Africa, British Prime Minister David Cameron himself mooted the idea of stopping rioters communicating via social media during riots in England in August.

William Echikson, Google's head of free expression in Europe, the Middle East and North Africa, warned at a side meeting of the conference that efforts to restrict online activity were not simply confined to undemocratic regimes.

Freedom of expression "is being challenged closer to home here in Europe. There are some 60 countries which impose controls now on the Internet, and that's up from two a decade ago," Echikson said.

He cited a case last year when three Google Italy executives were each given a six-month suspended sentence for violation of privacy over an Internet video showing a handicapped teenager being bullied in Turin.

"The dangers are really here in the present and they are threatening companies like Google," Echikson said.

The London talks will cover a broad agenda but the main item of interest is likely to be the closed-door discussions on international security, looking at how to manage cyber attacks on individuals, firms and governments.

A British ministerial advisor accused China and Russia on Monday of being behind many of the attacks, and both countries were represented in London.

The Chinese delegation includes officials from the ministries of foreign affairs, information technology and public security as well as the State Council Information Office, a spokesman for the Chinese embassy in London confirmed.

Hague said the aim of the conference would be to set up some basic global principles for cyberspace, including the need for universal access to the Internet and the need for governments to act "proportionately".

"In the place of today's cyber free-for-all, we need rules of the road," he said, adding that Hungary had agreed to hold a follow-on conference in 2012, and South Korea would hold another similar meeting in 2013.