The Philippines argued at a closed hearing on Tuesday that an international court should intervene in its dispute with China over the right to exploit natural resources and fish in the South China Sea.
Although China has declined to participate, the case at the Permanent Court of Arbitration in The Hague is being closely watched by Asian governments and Washington, given rising regional tensions as Chinese naval power grows.
A panel of five judges will hear arguments this week and decide whether the treaty-based court has jurisdiction.
Manila filed suit at the court in 2013, seeking to enforce its right to exploit waters in a 200-nautical mile "exclusive economic zone" off its coast, as defined under the UN Convention on the Law of the Sea.
The Philippines argues that the arbitration court is the correct venue for resolving disputes covered by the treaty, which both countries have signed.
"The Philippines believes the court has jurisdiction over all the claims it has made," said lawyer Paul Reichler, representing the Philippines.
He said he was confident the court would ultimately rule in the Philippines' favour.
Chinese Foreign Ministry spokeswoman Hua Chunying said China did not accept the court's jurisdiction and would not participate.
"China opposes any form of arbitration process proposed and promoted by the Philippines," Hua told a daily news briefing in Beijing on Tuesday.
In a position paper in December, China argued the dispute was not covered by the treaty because it was ultimately a matter of sovereignty, not exploitation rights.
China claims most of the South China Sea. The Philippines, Vietnam, Malaysia, Taiwan and Brunei claim overlapping parts of the strategic waterway.
While the hearings are closed to the public, the court said in a statement it had allowed small delegations from Vietnam, Malaysia, Japan, Indonesia and Thailand to observe proceedings after getting requests from those countries.
After the Philippines, the country most at odds with Beijing over the South China Sea is Vietnam. Japan is also involved in a bitter dispute with China over uninhabited islands in the East China Sea.
Manila says China is unfairly preventing it from accessing reefs and shoals that are under its dominion in the South China Sea.
Reichler said the case could continue even if China declined to participate. The court's rulings are binding, although it has no power to enforce them and countries have ignored them in the past.
Reichler declined to discuss the details of the Philippines' arguments on Tuesday.
Court legal counsel Judith Levine said the court would not comment on the proceedings.
Reichler said he expected a decision on jurisdiction within 90 days. A ruling on the merits of the case could take years.
