Haikou, formerly Hoikow, is the capital and most populous city of the Chinese province of Hainan. Haikou city is situated on the northern coast of Hainan, by the mouth of the Nandu River. The northern part of the city is on the Haidian Island, which is separated from the main part of Haikou by the Haidian River, a branch of the Nandu. Administratively, Haikou is a prefecture-level city, comprising four districts, and covering 2280 km2. There are 2,046,189 inhabitants in the built-up area, all living within the four urban districts of the city.