Chinese President Xi Jinping on Tuesday has officially opened the world's longest sea-crossing bridge. The bridge connects Hong Kong to Macau and the mainland Chinese city of Zhuhai.

The bridge spans 55 km including its access roads and has been constructed for aorund USD 20 billion. About 30 km of its total length crosses the sea of the Pearl River delta.

To allow ships through, a 6.7 km section in the middle dips into an undersea tunnel that runs between two artificial islands.

It's opening will cut travel time across the delta from several hours to just 30 minutes. It also forms a physical link between the mainland and the Asian financial hub, which was handed over from British to Chinese control in 1997.

President Xi attended the opening ceremony of the bridge in Zhuhai along with the leaders of Hong Kong and Macau.