The main line of the Shenzhen-Zhongshan Link, a mega cross-sea passage in the Guangdong-Hong Kong-Macao Greater Bay Area, has been fully connected after completion of the last part of the caisson concrete pouring on Tuesday morning.

The project, which integrates a bridge, island, tunnel and underwater interchange, starts from the Shenzhen airport interchange, crossing the Pearl River estuary to connect with Ma'anshan Island in Zhongshan.

It is the world's most comprehensive and difficult cross-sea cluster project, consisting of 24 kilometers of an eight-lane expressway with a traffic speed of 100 km per hour.

With completion of the link, the comprehensive transportation convenience of the GBA and the traffic capacity of the river crossing channel will be greatly improved, according to Deng Xiaohua, Party chief of Guangdong Transportation Group.

"After its opening to traffic next year, the Shenzhen-Zhongshan Link will help build a balanced and coordinated high-speed transportation network in the Pearl River estuary, along with other cross-sea and cross-river channels," said Deng.

The link is an important part of the national expressway network crossing the Pearl River estuary, about 30 km south of the Humen Bridge and 31 km north of the Hong Kong-Zhuhai-Macao Bridge, also a mega cross-sea passage in the GBA.

"The link will help lay a solid foundation for building a golden inner bay around the Pearl River estuary, providing more space for cooperation, development and imagination for cities along the line," said Deng.

The link is planned to be fully completed and opened to traffic next year, after construction of buildings, and mechanical and electrical facilities are completed. By then, the travel time from Zhongshan to Shenzhen will be shortened from the current two hours to less than 30 minutes.

The link has set several world records, including being the world's first long-distance dual eight-lane submarine tunnel using immersed tubes.

It has the world's longest and widest underwater steel shell concrete immersed tube tunnel, with an immersed tube section of about 5 km, which was connected and completed early in June.

Inside the tunnel on Tuesday, construction vehicles shuttled back and forth, and hundreds of workers were busy installing fireproof and decorative panels and other mechanical and electrical facilities.