GOOGLE'S fight with Chinese censors risks escalating into a fullblown US-China showdown over cyber warfare, as claims emerge about the unprecedented scale of Chinese attacks on US commercial and defence systems.

The Chinese-originated attack on Gmail accounts of human rights activists, which Google said had partly prompted its threat to leave China, was "probably insignificant" compared with the "theft" of source code and data from Google and at least 33 other leading technology companies, said a consultant briefed on the cyber attacks.

The details coincided with claims that the FBI had tracked more than 90,000 Chinese-originated attacks last year on the Defence Department alone.

Australia's big mining companies are refusing to negotiate iron ore contracts in China because of Chinese security agency intrusions at Rio Tinto, which culminated in the arrest of one of its executives, Stern Hu.