The Philippines has appealed to an international tribunal to declare China's claims to most of the South China Sea illegal, warning the integrity of United Nations' maritime laws is at stake.

In opening comments to the tribunal in the Hague on Tuesday, 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.

"In our view, it is also of utmost significance to the integrity of the convention, and to the very fabric of the legal order of the seas and oceans."

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.

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.

Tensions have risen sharply in recent years as a rising China has sought to stake its claims more assertively.

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 so-called nine dash line (based on an old map used by China) has no basis whatsoever under international law," he said.

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.

Del Rosario's comments, held in closed door proceedings but released by his office in Manila on Wednesday, were part of the Philippines' opening oral arguments.

China has refused to participate in the proceedings and said it will not abide by any ruling, even though it is has ratified the UN's Convention on the Law of the Sea.

However the Philippines hopes a ruling in its favour will pressure China into making concessions.

Any ruling from the tribunal is not expected until next year.