Haikou is the capital and most populous city of the Chinese province of Hainan. It lies on the northern coast of Hainan, at the mouth of the Nandu River. Administratively, Haikou is a prefecture-level city made up of four districts, covering 2,280 square kilometres (880 sq mi).
The northern part of the city occupies Haidian Island, which is separated from the main part of Haikou by the Haidian River, a branch of the Nandu. The built-up area has 2,046,189 inhabitants, all living within the four urban districts.