A US warship that was forced to manoeuvre to avoid a collision with a Chinese naval vessel had "posed a threat", state-run media said Monday, after Washington accused China of being the aggressor.

The Global Times newspaper, which often takes a nationalistic stance, said the USS Cowpens guided missile cruiser had "come to China's threshold and posed a threat to China's military security".

Washington issued a formal protest after the incident in the South China Sea between the Cowpens and a Chinese navy vessel on December 5, insisting that the ships were in international waters.

Beijing claims almost the whole of the South China Sea, even areas close to the coasts of other littoral states.

"If the American navy and air force always encroach near China's doorstep, 'confrontation' is bound to take place," the Global Times said. "As China's strength grows, the US should learn to communicate with and respect China if it doesn't want a collision on the sea or in the air."

The stand-off underscored tensions that escalated after Beijing last month declared an expanded "air defence identification zone" in the East China Sea.

Foreign ministry spokeswoman Hua Chunying referred questions on the incident to China's defence ministry.

But she added: "I can tell you in principle that China respects the freedom of navigation and overflight that is in accordance with international laws."

The near-miss at sea is the most significant maritime incident between the US and China since 2009, when five Chinese ships surrounded and harassed a US Navy surveillance ship in the same waters.

US naval officers and defence officials said last week that the Chinese ship had crossed directly in front of the Cowpens and halted less than 500 metres away, forcing the American ship to take evasive action to avoid a collision.

The Global Times quoted an anonymous Chinese military expert as saying the US "was tailing after and harassing" China's Liaoning aircraft carrier which was conducting drills in the area, and that the USS Cowpens had come within 45 kilometres of the "inner defence layer of the Chinese fleet".

"Bad guys always claim innocence first," the source told the paper, adding that the US warship "took offensive actions at first towards the Liaoning formation on the day of the confrontation".

Su Hao, a professor of Asia-Pacific studies at China Foreign Affairs University, defended the Chinese vessel's actions, saying they were necessary to protect Beijing's maritime rights.

"The Chinese took action only after the US vessels refused to comply with warnings," he told the China Daily newspaper.