Stretching nearly 30 kilometers, the world's longest cross-sea high-speed railway bridge across Hangzhou Bay in eastern #China, achieved a major construction milestone on Friday with the topping-out of its first main tower. Rising 200 meters above sea level, roughly the height of an 80-story building, the tower represents a significant engineering challenge due to the complex offshore conditions. Upon completion, the bridge is projected to set five world records in cross-sea railway engineering.