Territorial rivalry has escalated throughout the seas around China as regional and international navies seek to establish rights of passage against an expanding Chinese presence.
Chinese and Philippine vessels have been locked in a high seas stand-off since the PLA Navy prevented a Philippine warship from arresting crews of Chinese fishing boats near the Scarborough Shoal on April 8.
Both countries claim the fish rich shoal as their own and protests by Philippine fishermen over their loss of livelihood have drawn mass support in the south-east Asian country.
China International Travel Service, the state-owned tourism operator, yesterday suspended ties with the Philippines after organisers announced plans to demonstrate outside Chinese embassy buildings and property today.
Beijing also issued a travel advisory warning its citizens to keep a low profile. "Avoid going out at all if possible, and if not, to avoid going out alone," it said. "If you come across any demonstrations, leave the area, do not stay to watch."
Reports in Japan said five Chinese warships – including two guided missile destroyers, two frigates and a amphibious landing ship – had passed through waters close to Okinawa moving to Philippine reefs.
As the dispute escalated, Leon Panetta, the US defence secretary, met senators in a push to ratify a treaty that would bolster legal backing for US naval patrols in dispute regions such as the South China Sea.
Seizing on warnings of the dangers of escalating "gunboat diplomacy" Mr Panetta called on the senate to ratify the Laws of the Sea, a UN treaty that has been hindered by procedural disputes.
"By moving off the sidelines and leading the discussion, we would be able to influence those treaty bodies that develop and interpret the Law of the Sea," he said. "In that way, we would ensure that our rights are not whittled away by the excessive claims and erroneous interpretations of others."
American officials also announced the deployment of Littoral Combat Ships, a new generation of vessels that would allow the US much more extensive coverage of Asian sea lanes including the Strait of Malacca, as well as areas disputed by China.
The first of the shallow-draft ships, Freedom would be deployed to operate from Singapore for 10 months.