Chinese foreign ministry spokeswoman Hua Chunying said that the country respected freedom of navigation and overflight in the South China Sea, but would "firmly oppose infringement of sovereignty under that pretext", AFP reported.
Beijing says it has sovereign rights to nearly all of the South China Sea, including waters close to the coasts of other states.
The sea is a strategically vital waterway with shipping lanes through which about a third of all the world's traded oil passes, and the dispute has raised fears of clashes.
Hua's comments came after US Defense Secretary Ash Carter warned Beijing following a meeting of American and Australian officials Tuesday that Washington will continue to send its military "wherever international law allows", including the South China Sea.
Australia is a key Pacific ally of the US and its foreign minister Julie Bishop said the two countries were "on the same page" on the issue.
An editorial in the Global Times, which is close to China's ruling Communist party, condemned Washington's "ceaseless provocations and coercion".
"China mustn't tolerate rampant US violations of China's adjacent waters and the skies over those expanding islands," it said, adding that its military should "be ready to launch countermeasures according to Washington's level of provocation."
Coming within 12 nautical miles of the islands could be a "breach of China's bottom line", the paper said, warning: "If the US encroaches on China's core interests, the Chinese military will stand up and use force to stop it."