Beijing has declared war on the wave of "unhealthy" internet content it says is engulfing the nation’s cyberspace, amid fears China's young are being corrupted en masse by an influx of online sex and violence.

The nation's leading news sites and internet portals have vowed to adhere to a strict programme of "self-censorship" to support the "Eight Honours and Disgraces", a new doctrine of "socialist morality" recently laid out by Hu Jintao, the Chinese President.

The move is the latest in a string of initiatives by China designed to cement the government's already formidable hold over online content.

A pledge signed by 14 internet companies, including market leaders Sina Corp and Tom Online, voices concern over how the rapid growth of internet use in China has led to an explosion of pornographic content.

The companies are also aiming to address what is being seen in China as trends towards "internet addiction" by young people, online scams and spam e-mail.

The proposals have also been backed by 11 China-based news sites, including Xinhuanet.com and Chinadaily.com.cn, which said they would back "self-censorship" to "resist indecent content".

"At the same time as the web develops quickly, certain sites are transmitting unhealthy news ... and uncivilised voice services, including pornographic content that can be harmful to society," the document, written by the The Internet Society of China (ISC), says.

"We should run our business in a civilised way. We should not produce, disseminate and spread information that harms state security, social stability and information that violates laws and regulations and social morality," it added in a statement on the Sina Corp site.

"Unhealthy information has harmed the physical and mental health of children and minors. Such content poses a threat to social harmony and stability and the healthy and orderly development of the internet."

China already has a reputation for tough crackdowns on internet use it does not approve of.

In 2004, the Chinese government kicked off a massive campaign to weed out online pornography. In 2005, 11 people were jailed for up to 12 years for running an obscene website in China's largest case of internet pornography.

The latest move follows the publication of eight strictures by Mr Hu on how life should be led in China at a time of unprecedented change. The list includes exhortations to "serve the people" and to "know plain living and hard struggle" and to "not wallow in luxuries and pleasures" - directions designed to remind upwardly mobile Chinese that many of their countrymen remain desperately poor, despite the country’s rapid economic progress.

However, critics have identified a darker side to China's internet policing. The country has been labelled "the world champion" of internet censorship by Reporters Without Borders, the press freedom group.

The West's leading internet players, - Google, Microsoft, Yahoo! and eBay - have all been caught in the resulting controversy.

But the lure of China's prospects has offset fears of negative reactions from their domestic markets. Last week, Bill Gates, the Microsoft chairman and founder, hosted Mr Hu at a dinner during the politician's visit to America.

Eric Schmidt, the Google chief executive, used the recent relaunch of the company's brand in China to reaffirm his commitment to the territory and made it clear that Google has no intention of confronting China's ruling Communist Party over online restrictions.

China currently has at least 110 million internet users - an estimated 78 million are under 30 - ranking it second only to the United States. Some estimates place the number of users higher still and analysts are agreed the country will advance to the No1 spot.

According to the ISC, it received more than 120,000 complaints from the public last year, around 70 per cent of which were about pornography and 8 per cent over gambling scams.

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