The Philippines is considering inviting tourists to its biggest and most strategically important outpost in the South China Sea as part of efforts to assert its claim to sovereignty over some of the world's most contested islands.

Thitu island in the Spratly archipelago is in the midst of major upgrades to its dilapidated facilities, playing catch-up with China and Vietnam, which have been developing facilities on islands they either occupy or have built from scratch on top of submerged reefs.

"We are on track in rebuilding or repairing our runway in Pagasa," said Philippine Defense Secretary Delfin Lorenzana, referring to Thitu, some 280 nautical miles (about 519 kilometers) off the Philippine coast.