Photo taken on June 6, 2017 shows the Hong Kong-Zhuhai-Macao Bridge under construction. Major work on the 55-km-long Hong Kong-Zhuhai-Macao Bridge, the world's longest sea bridge, has passed authorities' evaluation. The huge project has been considered an engineering wonder and a magnificent feat of si-tech innovation. The bridge took six years of preparation, and eight years to build. Major work on the bridge consisted of a 22.9-km-long main bridge, a 6.7-km-long tunnel and an artificial island off the bridge, which was considered the most technically demanding part of the whole construction. The bridge will slash the travel time between Hong Kong and Zhuhai from three hours to just 30 minutes, further integrating cities in the Pearl River Delta. (Xinhua/Liang Xu)

BEIJING, Feb. 24 (Xinhua)-- A bridge linking Hong Kong, Zhuhai and Macao has moved a step closer to official opening, with a major tunnel project fully completed Saturday.

The 2,741-meter-long Gongbei Tunnel is 21 meters high with an excavation area of 336.8 square meters, bigger than any other highway tunnel in the world, China Railway Construction Corporation (CRCC) said.

The 55-kilometer Hong Kong-Zhuhai-Macao Bridge, situated in the Lingdingyang waters of the Pearl River Estuary, will be the world's longest sea bridge.

The two-way tunnel with six lanes in total, which has been built over five years, is the only passage connecting the main body of the bridge with Zhuhai, according to the company.

The full completion of the tunnel has "laid a foundation for the bridge to be officially open to traffic," said the CRCC, giving no specific timetable.

Comprising a main bridge structure together with crossing facilities and link roads, it is designed to meet the growing demand of passenger and freight land transport between the three cities.

The bridge will slash travel time between Hong Kong and Zhuhai from three hours to just 30 minutes, further integrating cities in the Pearl River Delta.