\" \" A bird's-eye view of the Hong Kong-Zhuhai-Macao Bridge in Zhuhai, Guangdong, China. TPG/Getty ImagesThe world's longest sea-crossing bridge has opened, connecting mainland China to Hong Kong. Officially known as the Hong Kong-Zhuhai-Macao Bridge, the structure consists of three cable-stayed bridges, an undersea tunnel and four artificial islands. By comparison, that's 4.5 times the amount of steel in San Francisco's Golden Gate Bridge, according to Travel Wire Asia. In 1997, Hong Kong — a former British territory — became a special administrative region of the People's Republic of China.