Hǎikǒu, 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.Administratively, Haikou is a prefecture-level city, comprising four districts, and covering 2,280 square kilometres. There are 2,046,189 inhabitants in the built up area all living within the 4 urban districts of the city.Haikou was originally a port city. Today, more than half of the island's total trade still goes through its ports. The city is home to Hainan University, which has its main campus on Haidian Island.