In opening comments to the tribunal in the Hague on yesterday, Foreign Secretary Albert del Rosario said the Philippines had sought judicial intervention because China's behaviour had become increasingly "aggressive" and negotiations had proved futile.
Del Rosario said the UN's Convention on the Law of the Sea, which the Philippines and China have both ratified, should be used to resolve their bitter territorial dispute.
"The case before you is of the utmost importance to the Philippines, to the region, and to the world," del Rosario told the tribunal.
China insists it has sovereign rights to nearly all of the South China Sea, a strategically vital waterway with shipping lanes through which about a third of all the world's traded oil passes.
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Its claim, based on ancient Chinese maps, reaches close to the coasts of its southern neighbours.
The Philippines, Vietnam, Malaysia, Brunei and Taiwan also have claims to parts of the sea, which have for decades made it a potential military flashpoint.
Following a stand-off between Chinese ships and the weak Filipino Navy in 2012, China took control of a rich fishing ground called Scarborough Shoal that is within the Philippines' exclusive economic zone.
China has also undertaken giant reclamation activities that have raised fears it will use artificial islands to build new military outposts close to the Philippines and other claimants.
China has rejected all criticism over its actions, insisting it has undisputed sovereign rights to the sea.
However del Rosario told the tribunal in the Hague that China's argument of claiming the sea based on "historic rights" was without foundation.
The Philippines submitted its case to the Hague-based Permanent Court of Arbitration, a 117-state body that rules on disputes between countries, in early 2013.