Intercity bus services run by multiple private companies connect all major cities. They are the most popular means of transportation followed by the rail service ''Camrail''. Rail service runs from Kumba in the west to Bélabo in the east and north to Ngaoundéré. International airports are located in Douala and Yaoundé, with a third under construction in Maroua. Douala is the country's principal seaport. In the north, the Bénoué River is seasonally navigable from Garoua across into Nigeria.