Macau (; ), also spelled Macao, officially known as the Macao Special Administrative Region of the People's Republic of China, is a special administrative region on the southern coast of the People's Republic of China. Macau lies on the western side of the Pearl River Delta across from Hong Kong, which is about 64 kilometers to the east, and it is also bordered by Guangdong of Mainland China to the north and the South China Sea to the east and south. With an estimated population of around 636,200 living in an area of 30.3 km² (11.6 sq mi), it is the most densely populated region in the world.