The Hong Kong-Zhuhai-Macau Bridge is a 55-kilometer bridge-tunnel system connecting the three major cities of Hong Kong, Zhuhai, and Macau. It is the longest sea-crossing bridge in the world, featuring a 6.
From Wikipedia
The Hong Kong–Zhuhai–Macau Bridge (HZMB) is a 55-kilometre (34 mi) bridge–tunnel system consisting of a series of three cable-stayed bridges, an undersea tunnel, and four artificial islands. It is both the longest sea crossing and the longest open-sea fixed link in the world. The HZMB spans the Lingding and Jiuzhou channels, connecting Hong Kong and Macau with Zhuhai—a major city on the Pearl River Delta in China.