With the finishing of its undersea tunnel, the main structure of the world's longest sea bridge, which links Hong Kong, Zhuhai and Macao, was completed on Friday. The 40-meter-deep undersea tunnel creates a gap in the bridge to allow cargo ships to pass through into the Pearl River Delta.

A Y-shaped bridge, the main structure is 29.6 kilometers in length, consisting of a 22.9-km bridge section and 6.7-km underground tunnel. The total length of the bridge is 55 kms.

It consumed 420,000 tons of steel, enough to build 60 Eiffel Towers, and 1.08 million cubic meters of cement.

The Hong Kong-Zhuhai-Macao Bridge is due open to traffic at the end of this year. It will cut travel time between Hong Kong and Zhuhai from three hours to just 30 minutes, further integrating the cities in the Pearl River Delta.

It has taken seven years to build, at an estimated cost of $10.6 billion.

The project is part of the plan to develop the Guangdong-Hong Kong-Macao Greater Bay Area.