Hǎikǒu (Chinese: 海口), is the capital and most populous city of Hainan province, People's Republic of China. It is situated on the northern coast of Hainan, by the mouth of the Nandu River. The northern part of the city is the district of Haidian Island, which is separated from the main part of Haikou by the Haidian River, a branch of the Nandu.