The 55-kilometer Hong Kong-Zhuhai-Macao Bridge is completed on September 27, 2016, making it the longest cross-sea bridge in the world. [Photo: Chinanews.com]

With an investment of around 105 billion yuan (15.7 billion US dollars), the 89-kilometer-long project includes the 55-km bridge, a tunnel and artificial islands.

The length makes it one of the most challenging projects currently under construction worldwide.

The Hong Kong-Zhuhai-Macao Bridge, completed on Tuesday, will greatly reduce the travel time between Zhuhai and Hong Kong, from over three hours by car or around one hour by sea, to less than 30-minute driving.

The project is part of China's planned national highway network, linking the western and eastern banks of the Pearl River.

It will also allow a circumnavigation of the three cities for the first time, taking approximately one hour.