Hong Kong, officially the Hong Kong Special Administrative Region of the People's Republic of China, is an autonomous territory on China's south coast. It has an area of 1,104 km2 and shares its northern border with the Guangdong Province of Mainland China. With around 7.2 million Hong Kongers of various nationalities, Hong Kong is the world's fourth most densely populated country or territory.
Hong Kong used to be a British colony with the perpetual cession of Hong Kong Island from the Qing Empire after the First Opium War (1839–42). The colony expanded to the Kowloon Peninsula in 1860 and acquired a 99-year lease of the New Territories from 1898. Hong Kong was later occupied by Japan during the Second World War until British control resumed in 1945. The Sino-British Joint Declaration signed between the United Kingdom and China in 1984 paved way for the transfer of sovereignty of Hong Kong in 1997, when it became a special administrative region (SAR) of the People's Republic of China with a high degree of autonomy.
Under the principle of "one country, two systems", Hong Kong maintains a separate political and economic system from China. Except in military defence and foreign affairs, Hong Kong maintains its independent executive, legislative and judiciary powers. In addition, Hong Kong develops relations directly with foreign states and international organisations in a broad range of "appropriate fields". Hong Kong involves in international organizations, such as the WTO and the APEC, actively and independently.
Hong Kong is one of the world's most significant financial centres, with the highest Financial Development Index score and consistently ranks as the world's most competitive and freest economic entity. As the world's 8th largest trading entity, its legal tender, the Hong Kong dollar, is the world's 13th most traded currency. As the world's most visited city, Hong Kong's tertiary sector dominated economy is characterised by competitive simple taxation and supported by its independent judiciary system. Even with one of the highest per capita incomes in the world, it suffers from severe income inequality.
Nicknamed "Pearl of the Orient", Hong Kong is renowned for its deep natural harbour, which boosts the world's fifth busiest port with ready access by cargo ships, and its impressive skyline, with the most skyscrapers in the world. It has a very high Human Development Index ranking and the world's longest life expectancy. Over 90% of the population makes use of well-developed public transportation. Seasonal air pollution with origins from neighbouring industrial areas of Mainland China, which adopts loose emissions standards, has resulted in a high level of atmospheric particulates in winter.