China has completed the construction of two lighthouses in the disputed South China Sea, the official Xinhua news agency reported, as tensions in the region mount over Beijing's maritime ambitions. A completion ceremony was held for the lighthouses on Cuateron Reef and Johnson South Reef in the Spratly islands. The United States and the Philippines have opposed the construction. China claims most of the energy-rich South China Sea, through which $5 trillion in ship-borne trade passes every year, and the Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping claims. The issue is central to increasingly tense relations between the United States and China, the world's two largest economies.