Updated

The Philippines' top diplomat says any move by China to transform a Manila-claimed shoal into an island would be a "game-changer" in blossoming relations although he says Beijing has pledged not to undertake any construction in the strategically located area of the South China Sea.

Foreign Secretary Perfecto Yasay Jr. said in response to a reporter's question Thursday that any Chinese construction in Scarborough Shoal would be "a very serious, provocative act" that would undermine the Philippine claim to the rich fishing area.

Five months after President Rodrigo Duterte made a state visit to China, Yasay disclosed for the first time that Chinese President Xi Jinping had told the Philippine leader during their meetings that China had no plans to build on Scarborough. Duterte has prioritized economic engagement with China.