Beijing: The Sydney Morning Herald's Web site, www.smh.com.au, may have fallen victim to China's attempts to control domestic access to foreign Internet sites.

The Herald site has been unavailable through Chinese Internet service providers (ISPs) for more than two weeks. Callers to the Herald bureau in Beijing have said they have been unable to access it since soon after the Olympics.

Other Australian media sites, including those of The Australian Financial Review and The Australian, remain available.

Sources in the Ministry of Information Industry, which supervises network access in China, have confirmed that the Herald site cannot be traced into the domestic network. But no government agency appears willing or able to shed any light on why.

The Foreign Ministry, the Public Security Bureau and the agencies responsible for network access have all denied knowledge of or responsibility for a block on the site. The Herald's sister paper, The Age, has been unreachable via Chinese ISPs for more than a year. Fairfax's F2 site remains unaffected.

China routinely blocks the Web sites of certain overseas news organisations. The New York Times and The Washington Post are rarely accessible, and the CNN and the BBC sites are also often barred.

Human rights sites critical of the Government are also blocked.

In August the People's Daily, the mouthpiece of the Communist Party, called on official media to strengthen their "political thought work" in the face of a flood of information available via the Internet, which it described as a "thought and public opinion battle front".

"Enemy forces at home and abroad are sparing no effort to use this battle front to infiltrate us," the paper said.

The Internet poses a problem for China's political leaders, who are in two minds about the free flow of information it makes possible.

A number of domestic sites that challenged the Government have been closed this year.

Aside from political "Web dissidents", China has also targeted the banned Falun Gong spiritual and meditation movement, pornography and criminal activity.

The most recent figures indicate there are at least 17million Internet users in China - slightly more than 1per cent of the population. The China National Network Information Centre says the number doubled in the first half of this year.

It is expected that China will become the world's largest Internet market in the next five years.