Taiwan has rejected the Arbitral Tribunal's ruling, saying its conclusion that Taiping Island and other features in the Spratlys are rocks is not "legally binding".
President Tsai Ing-wen is expected to comment on the ruling this morning during a sendoff for the crew of a frigate leaving for Taiping Island.
The 46ha outcrop, about 2,000km south of Taipei, is the biggest feature in the Spratlys and is home to some 200 Taiwanese coast guard personnel and researchers. Taiping Island is also known as Itu Aba in the Philippines.
The Foreign Ministry said last night that the ruling is "completely unacceptable" and has "no legally binding force". Taiwan "will take resolute action to safeguard" its territory and maritime rights, it added.
The previous government had launched a high-profile drive to present Taiping Island as an "island", which is entitled to a 200-nautical-mile exclusive economic zone.
Urging the government not to accept the ruling yesterday, Mr Huang Hung-yen, deputy director-general of the Fisheries Agency, said the waters surrounding Taiping Island are "an important fishing ground" for Taiwanese fishermen.