Shenzhen is a prefecture-level city in the province of Guangdong, China. A special economic zone, it is located on the east bank of the Pearl River estuary on the central coast of Guangdong, bordering Hong Kong to the south, Dongguan to the north, Huizhou to the northeast, and Macau to the southwest. With a population of 17.5 million in 2020, Shenzhen is the third-most-populous city by urban population in China after Shanghai and Beijing. The Port of Shenzhen is the world's fourth-busiest container port. Shenzhen roughly follows the administrative boundaries of Bao'an County, which was established in imperial times. As a result of the Opium Wars, the southern portion of Bao'an County was ceded to Britain and became part of British Hong Kong, while the village of Shenzhen was next to the border. Shenzhen turned into a city in 1979. In the early 1980s, the reform and opening up introduced by Deng Xiaoping resulted in the city becoming the first special economic zone of China due to its close proximity to Hong Kong, attracting foreign direct investment and migrants searching for opportunities. In thirty years, the city's economy and population boomed and has since emerged as a hub for technology, international trade, and finance. Shenzhen is home to the Shenzhen Stock Exchange, one of the largest stock exchanges in the world by market capitalization, and the Guangdong Free-Trade Zone.