The main span of the Hong Kong-Zhuhai-Macao Bridge was completed on June 29, 2016.[Photo by Lin Guiyan for China Daily]

The Hong Kong-Zhuhai-Macao Bridge moved a step closer to completion on Wednesday morning as two main bridge structures were connected.

Lawmaker Lo Wai-kwok, who represents the engineering sector in the city's legislature, described the connection as "a milestone for the world-class project" but said there will still be many challenges before the project is finished.

The Hong Kong-Zhuhai-Macao Bridge Authority said 80 percent of a 6.7-km tunnel has been completed.

A full-scale effort can now begin on the bridge deck pavement and traffic engineering.

The 55-km link is comprised of the offshore bridge and tunnel, boundary crossing facilities in Hong Kong, Zhuhai and Macao, and routes connecting the three cities. The main structure of the bridge is made up of the underwater tunnel and a bridge spanning 22.9 km. Artificial islands will be built at both ends of the tunnel.

According to the authority, the amount of iron used in the main structure alone weighs around 400,000 metric tons, enough for about 60 Eiffel Towers.

Lo said every part of the project is challenging in its own way, and said that technical issues involving the underwater tunnel construction caused delays. "Luckily they have been solved and will be finished soon," Lo said.

The completion of the Hong Kong section of the bridge, built independently by the Hong Kong SAR government, was postponed for a year to the end of 2017, after it was reported that the artificial islands had shifted between six and seven meters in September.

Lo explained that the shift, caused by movement of sea mud, will not lead to further delays, and the construction of other facilities on the artificial land are proceeding as usual.

"Everyone is striving to complete the project by the end of 2017, despite different difficulties in constructing their own parts in three cities," Lo said.

The bridge, planned in 1983, is expected to be completed by the end of next year at the earliest. Once the bridge is completed, commuting times between Hong Kong and Zhuhai will be reduced from 3 1/2 hours to only 30 minutes.