Beijing: China has deployed a defensive missile system on the Spratly Islands in the South China Sea, the Chinese foreign ministry has confirmed.

The installation of anti-ship cruise missiles and surface to air missile systems on three islands west of the Philippines was first reported by American television network CNBC this week, quoting unnamed sources.

Fiery Cross Reef in January 2018 - one of the locations of the missile deployments. Credit:CSIS/AMTI Digital Globe

Media reports from the US prompted Australia's Foreign Minister Julie Bishop to warn any military build-up would run counter to China's commitments.

"If the media reports are accurate, then the Australian government would be concerned because this would be contrary to China's stated aspiration that it would not militarise these features," Bishop said.