Hong Kong officially the Hong Kong Special Administrative Region of the People's Republic of China (HKSAR), is a metropolitan area and special administrative region of the People's Republic of China on the eastern Pearl River Delta of the South China Sea. With over 7.5 million residents of various nationalities in a 1,104-square-kilometre (426 sq mi) territory, Hong Kong is one of the most densely populated places in the world. Hong Kong became a colony of the British Empire after the Qing Empire ceded Hong Kong Island at the end of the First Opium War in 1842. The colony expanded to the Kowloon Peninsula in 1860 after the Second Opium War and was further extended when Britain obtained a 99-year lease of the New Territories in 1898. The whole territory was transferred to China in 1997. As a special administrative region, Hong Kong maintains separate governing and economic systems from that of mainland China under the principle of "one country, two systems"