At the time of the 1991 census, Hong Kong had a population of 5,674,114. The 2001 population was 7,210,505, indicating a population density of 6,603 persons per sq km (17,102 per sq mi). The population is unevenly distributed, however, with the greatest concentrations of people in Kowloon and across the harbor on Hong Kong Island. Some districts, such as Mong Kok in Kowloon, have population densities of about 40,000 persons per sq km (about 100,000 per sq mi), among the highest urban densities in the world. Although birth and death rates are comparatively low in Hong Kong, migration from other parts of China creates a high population growth rate, and migrants now make up about 40 percent of the population.

Lowlands of the Hong Kong region, including floodplains, river valleys, and reclaimed land, occupy less than one-fifth of the land. Extensive lowland regions are found only north of Mount Tai Mo, in the Yuen Long and Sheung Shui plains. The urban area that spans the two sides of the harbour, with continued reclamation, takes up only about one-tenth of the level area.