Haikou is the capital and most populous city of Hainan province in China. It is located on the northern coast of the island by the mouth of the Nandu River. The city's geography is defined by Haidian Island, which occupies the northern part of the city and is separated from the main urban area by a branch of the Nandu River known as the Haidian River.
Administratively, Haikou is classified as a prefecture-level city covering an area of 2,280 square kilometres. The city comprises four districts, with a built-up population of 2,046,189 inhabitants residing within these urban boundaries.