An international tribunal is to begin deliberations on whether it can hear a legal challenge over territorial claims in the South China Sea.
In 2013, the Philippines asked the Permanent Court of Arbitration to declare invalid most of China's maritime claims in the disputed area.
China claims almost the whole of the South China Sea angering several Asian neighbours.
It says the tribunal does not have the jurisdiction to hear the challenge.
If the tribunal decides it can rule on the case, the legal hearings will get under way.
The Philippines has sent a high-profile legal team to the proceedings by the five-member tribunal which will continue till 13 July. China is not participating in the arbitration.
Vietnam, Taiwan, Malaysia, Brunei and Indonesia also have claims in the 3.5 million-sq-km (1.4 million-sq-mile) area said to be rich in resources.
The Philippines has had diplomatic spats with China over the Scarborough Shoal and Spratlys in particular.
It say China's "nine-dash line", which China uses to demarcate its territorial claims, is unlawful under the UN Convention on the Law of the Sea, which both countries have signed, and wants the tribunal to declare it invalid.
Analysis: Carrie Gracie, BBC News, China editor
It's a David and Goliath struggle at an international tribunal in The Hague on Tuesday. Or it would be if Goliath had turned up.
In 2010, China's then foreign minister, Yang Jiechi, told uneasy neighbours: "China is a big country, other countries are small countries, and that's just a fact."
But size is not legal currency when it comes to competing claims in the South China Sea. The five judges in the Court of Arbitration will decide the case of the Philippines versus the People's Republic of China, according to the United Nations Convention on the Law of the Sea (UNCLOS) to which both countries are signatories.
Legal challenges are cheaper than military build-up, and a more level playing field for the tiny Philippines against its giant neighbour.
In recent months China has been doing aggressive land reclamation and building of facilities on several reefs, prompting the United States to call for a halt on such efforts.
Satellite images show that, among other things, China is building an airstrip on reclaimed land on Fiery Cross Reef in the Spratly Islands.
China has argued that it is acting lawfully based on its sovereign rights to the disputed areas.