SINGAPORE — China is already one of the world's largest offshore energy producers. It wants to become bigger still by finding more oil and natural gas in home waters or in zones close to China, to avoid becoming excessively dependent on foreign imports.

However, China's evolving energy security strategy could further complicate its relations with Southeast Asia, and with countries like Japan, the United States and South Korea that regard the South China Sea as an international highway for trade and free movement of military planes and ships.

A major focus of Beijing's offshore search for energy to fuel its rapid economic growth is on the South China Sea, where it has overlapping territorial claims with Vietnam, the Philippines, Malaysia and Brunei.