Australia's intelligence agencies believe China is hiding the extent of a massive military build-up that goes beyond national defence and threatens regional stability, the latest WikiLeaks cables show.

A strategic assessment by the agencies found that China's military spending for 2006 was $90 billion - double the $45 billion budget publicly announced by Beijing, Fairfax newspapers report.

"China's longer-term agenda is to develop 'comprehensive national power', including a strong military, that is in keeping with its view of itself as a great power," a copy of the secret assessment provided by Foreign Affairs officials to the US embassy in Canberra said.

"We agree that the trend of China's military modernisation is beyond the scope of what would be required for a conflict over Taiwan.

"Arguably China already poses a credible threat to modern militaries operating in the region and will present an even more formidable challenge as its modernisation continues."

The 2006 Australian intelligence assessment was contained in a US embassy cable obtained by WikiLeaks and provided to Fairfax newspapers.

The assessment also warned that factors including China's rising nationalism and difficulties with Japan meant that "miscalculations and minor events could quickly escalate".

- AAP