BEIJING -- 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.