The prospect of a four-country bloc patrolling together in the waters would send a unified message to China, which maintains a constant presence of hundreds of vessels across the South China Sea to assert its claims.

Taiwanese forces have closely monitored China's moves, scrambling fighter jets and deploying warships to keep guard against the Chinese navy.

Drills have included launches of ballistic missiles, some of which flew over the island's capital of Taipei, and simulated sea and air attacks in surrounding skies and waters.