A United Nations tribunal is set to hear a legal challenge by the Philippines against China’s territorial claims in the South China Sea.
The Philippines says most of China’s maritime claims in the hotly disputed area are invalid.
In 2013, it began proceedings with the Permanent Court of Arbitration in The Hague, Netherlands.
China, which has rejected the case, is reclaiming land in the area prompting fears it is consolidating its claims.
China claims almost the whole of the South China Sea angering several Asian neighbours.
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 locked horns 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.
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.
Analysis: Carrie Gracie, BBC News, China editor
It’s a David and Goliath struggle at a United Nations 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.