Macau, also spelled Macao, officially the Macao Special Administrative Region of the People's Republic of China, is an autonomous territory on the western side of the Pearl River Delta in East Asia. Macau is bordered by the city of Zhuhai in Mainland China to the north and the Pearl River Estuary to the east and south. Hong Kong lies about 64 kilometres (40 mi) to its east across the Delta. With a population of 650,900 living in an area of 30.5 km2 (11.8 sq mi), it is the most densely populated region in the world.
Macau was administered by the Portuguese Empire and its inheritor states from the mid-16th century until late 1999, when it constituted the last remaining European colony in Asia. Portuguese traders first settled in Macau in the 1550s. In 1557, Macau was leased to Portugal from Ming China as a trading port. The Portuguese Empire administered the city under Chinese authority and sovereignty until 1887, when Macau, through a mutual agreement between the two countries, became a colony. Sovereignty over Macau was transferred back to China on 20 December 1999. The Joint Declaration on the Question of Macau and Macau Basic Law stipulate that Macau operate with a high degree of autonomy until at least 2049, fifty years after the transfer.