The aerial photo taken on June 29, 2016 shows the construction site of the main bridge parts of the Hong Kong-Zhuhai-Macao Bridge, the world's longest cross-sea bridge, in Zhuhai, south China's Guangdong Province. Two main bridge sections of the Hong Kong-Zhuhai-Macao Bridge joined together on Wednesday. (Xinhua/Liang Xu)

The world's longest cross-sea bridge HK-Zhuhai-Macao Bridge was successfully joined early Thursday morning, according to authorities of the bridge. 

Starting from the Lantau Island in Hong Kong, the Y-shaped bridge will have a total length of about 55 km, including a 6.7 km underwater tunnel and a 23-km bridge over the sea, making it the longest cross-sea bridge in the world.

The bridge will serve as an important channel linking Hong Kong, Macao, Zhuhai and the western part of the Pearl River Delta, one of the most economically-developed areas in the Chinese mainland.

Construction of the bridge started in 2009 at a cost of some 10 billion yuan or 1.5 billion US dollars. Once in operation, the bridge will shorten the four-hour drive from Hong Kong to Zhuhai in Guangdong to half an hour.

The aerial photo taken on June 29, 2016 shows the construction site of the main bridge parts of the Hong Kong-Zhuhai-Macao Bridge, the world's longest cross-sea bridge, in Zhuhai, south China's Guangdong Province. Two main bridge sections of the Hong Kong-Zhuhai-Macao Bridge joined together on Wednesday. (Xinhua/Liang Xu)

Photo taken on Sep. 6 shows construction of all piers holding up the Hong Kong-Zhuhai-Macao Bridge have been completed, which means the construction work has entered the final stage. It is scheduled to be finished in late 2016. (Xinhua Photo)

Design sketch of the bridge/ File Photo