The Philippines and Vietnam are forging closer ties in a symbolic move after China stepped up activities in disputed areas of the South China Sea, raising tension in the potential flash point.

China claims almost the entire South China Sea, believed to be rich in oil and gas deposits and fishery resources. Brunei, Malaysia, the Philippines, Vietnam and Taiwan also claim parts of the sea, crossed by ships carrying $5 trillion a year in cargo.

Pham Binh Minh, Hanoi's deputy prime minister and foreign minister, on Thursday began a day-two visit to Manila for talks to build a strategic partnership and strengthen security, trade and cultural ties.