An international tribunal on Tuesday began hearing a case brought by the Philippines over disputed islands in the South China Sea, in an increasingly bitter row with China.
The Permanent Court of Arbitration "commenced the hearing on the merits and remaining issues of jurisdiction and admissibility," the Hague-based tribunal said in a statement.
Manila has called for the tribunal, which is more than a century old, to rule on the dispute, appealing to the UN Convention on the Law of the Sea.
China, which claims economic and territorial rights in almost the entire South China Sea, has boycotted the proceedings and rejects the court's authority in the case.
"Our position is clear: we will not participate to or accept the arbitration," China's Foreign Ministry spokesman Hong Lei told a regular briefing earlier Tuesday.
The hearing, expected to last until November 30, is being held behind closed doors. But Australia, Indonesia, Japan, Malaysia, Singapore, Thailand and Vietnam are allowed to have observers present.
Experts say that a ruling could influence other cases in the heated South China Sea dispute - involving Vietnam, Malaysia, Brunei and other countries. Indonesia has signaled that it may also go to the court to counter an increasingly assertive China.
"We are confident that we will get a favorable decision on some of the issues, but it would be unrealistic to expect that we will get a favorable decision on all issues," Philippine Foreign Ministry spokesman Charles Jose said in Manila.
The Philippines will make submissions on 15 claims during the proceedings. China says that the legal challenge could delay a negotiated settlement between the two countries.
Court rulings are supposed to be binding on its member countries, which include China. But the tribunal, set up in 1899 as one of the first international judicial institutions, has no powers of enforcement and its rulings have been ignored before.
Following a stand-off between Chinese ships and the weak Philippine Navy in 2012, China took control of a rich fishing ground called Scarborough Shoal that is within the Philippines' claimed exclusive economic zone.
The waters - also claimed in part by Vietnam, Malaysia, the Philippines and Brunei - have become the stage for a tussle for dominance between Beijing and Washington, the world's two largest economic and military powers.
The United States, traditionally the region's dominant security player, also objects to China's moves, sending military aircraft to survey China's development activities.
Beijing has in recent years rapidly built artificial islands, which neighbors fear will be used as military outposts. Manila hopes that a ruling in its favor from the court, which was established in 1899, could put pressure on Beijing to rein in its territorial ambitions.
In a July hearing in The Hague, Philippine Foreign Secretary Albert del Rosario warned the very integrity of UN maritime laws was at stake. China's behavior had become increasingly "aggressive" and negotiations had proved futile, del Rosario said.
Manila earlier argued that China's territorial claims in the South China Sea violated the country's maritime rights under 1982 United Nations Convention on the Law of the Sea.