Tianjin is a metropolis in North China and one of the five national central cities. It is governed as a direct-controlled municipality, one of four such designations, and is thus under direct administration of the central government. The city borders Hebei Province and Beijing Municipality, bounded to the east by the Bohai Gulf portion of the Yellow Sea. As a dual-core city, Tianjin is divided into the old city and the Binhai New Area. As a treaty port since 1860, Tianjin has been a major seaport and gateway to the nation's capital.