Hong Kong is one of two Special Administrative Regions (SARs) of the People's Republic of China (PRC), the other being Macau. With a land mass of 1,104 km2 (426 sq mi), Hong Kong is one of the most densely populated areas in the world. Hong Kong's population is 95 percent ethnic Chinese and 5 percent from other groups. Hong Kong became a colony of the British Empire after the First Opium War (1839-42). Originally confined to Hong Kong Island, the colony's boundaries were extended in stages to the Kowloon Peninsula in 160 and then the New Territories in 1898. It was occupied by Japan during the Pacific War, after which the British resumed control until 1997, when China resumed sovereignty.