Australia has warned a Chinese base in Cambodia would upend peace and stability in the region, as the superpower moves to use debt-laden developing nations to expand its military footprint.

The apparent discovery by US intelligence services of a secret deal to station Chinese troops, store weapons and berth warships at the Ream Naval Base has alarmed the Morrison government, which has raised its concerns directly with Cambodia amid growing fears over Beijing's reach into South East Asia and the Pacific.

A military base on the Gulf of Thailand would give China more ability to assert contested territorial claims and economic interests in the South China Sea, and cement suspicions that it is using a wave of multi-billion dollar infrastructure projects to have more control over the waters to Australia's north.

The Sydney Morning Herald and The Age have been told Australia has sought information from the Cambodian government following a report by the Wall Street Journal - which was rejected by Cambodia and China as "fake news" - about plans for the 62-acre joint base.