China is asserting an idea of sovereignty over the South China Sea which is completely inconsistent with how the UN Convention on the Law of the Sea is understood, says Acting Prime Minister and Defence Minister Richard Marles.

"What UN Convention on the Law of the Sea provides for is freedom of navigation across the high seas around the world but in respect of that body of water particularly," Mr Marles told Sky News Australia.

"If you look at the South China Sea – China is seeking to shape the world around it in a way that we've not seen before."