The captain of a US supercarrier said Thursday the US Navy's presence in Asia would help safeguard "freedom of navigation", amid China's claims to sovereignty over vast waters in the region.

The commander of the USS George Washington, which is on a port call to the Philippine capital, said the United States was not taking sides in territorial disputes but stood firmly for keeping sea lanes open.

"One of the reasons we deploy throughout the region is so we can carry forth the banner of freedom of navigation. It is very important to us given the trade that travels throughout the region on the seas," Captain Gregory Fenton said.

However Fenton emphasised his ship's visit to Manila was a routine event and not related to the recent tensions between the Philippines, a close US ally, and China over rival claims to parts of the South China Sea.

He told reporters aboard the Japan-based carrier that the United States took no sides and hoped the countries involved would settle the disputes diplomatically.

The Philippines has been moving closer to the United States, its main defence ally, since a stand-off began in April with China over the Scarborough Shoal in the South China Sea.

China claims the shoal as well as nearly all of the South China Sea, even waters close to the coasts of neighbouring countries. The Philippines says the shoal is well within its 200-nautical-mile exclusive economic zone.

The South China Sea is the main maritime link between the Pacific and Indian oceans, giving it enormous trade and military value.

Most of the seaborne trade, including of oil and gas, between Europe and the Middle East and East Asia passes through the sea.

Aside from China and the Philippines, Vietnam, Taiwan, Malaysia and Brunei also have claims to the parts of the sea.

The USS George Washington's public affairs officer, Lieutenant Commander James Stockman, said the vessel had passed through the South China Sea on its way to the Philippines.