US warship challenges China Sea claims

A US warship has sailed close to disputed islands in the South China Sea to "challenge excessive maritime claims", US officials say.

A US navy destroyer has sailed through the South China Sea, challenging China's claims to the area. Source: AAP

A US navy destroyer has sailed near islands claimed by China in the South China Sea, drawing a warning from Chinese warships to leave the area.

The US action was the latest attempt to counter what Washington sees as Beijing's efforts to limit freedom of navigation in the strategic waters, US officials said after Friday's traverse.

The Chinese Defence Ministry called the move "illegal" and "provocative," saying that two Chinese warships had warned the US destroyer to leave.

The guided-missile destroyer USS Decatur challenged "excessive maritime claims" near the Paracel Islands, among a string of islets, reefs and shoals over which China has territorial disputes with its neighbours, the US officials said, speaking on condition of anonymity.

The destroyer sailed within waters claimed by China, close to but not within the 12-nautical-mile territorial limits of the islands, the officials said.

The Pentagon said the Decatur "conducted this transit in a routine, lawful manner without ship escorts and without incident." One official said the ship, which sailed near Triton and Woody Islands, was shadowed by three Chinese vessels and that all interactions were safe.

"This operation demonstrated that coastal states may not unlawfully restrict the navigation rights, freedoms and lawful uses of the sea that the United States and all states are entitled to exercise under international law," White House spokesman Josh Earnest said at a news briefing.

It was the fourth challenge that the United States has made to what it considers overreaching maritime claims by China in the South China Sea in the past year, and the first since May.

China, Washington's main strategic rival in Asia, claims almost the entire South China Sea, through which about $US5 trillion worth of trade passes each year. The United States has criticised Beijing's build-up of military facilities in the sea and expressed concerns they could be used to restrict free movement.

China has a runway on Woody Island, the site of the largest Chinese presence on the Paracels, and has placed surface-to-air missiles there, according to US officials. Taiwan and Vietnam also have claims on the Paracels.

The latest operation comes just after the volatile president of the Philippines announced, during a visit to China, his "separation" from Washington and realignment with Beijing. The Philippines has been a key ally of the United States and a territorial rival of Beijing in the South China Sea. Rodrigo Duterte took office as Philippine president in June.

Duterte's announcement on Thursday was a significant turnaround after a tribunal in The Hague ruled that China did not have historic rights to the South China Sea in a case brought by the previous Philippine administration and strongly backed by the United States.