The bridge has been built above Lingdingyang at the Pearl River Estuary, which has complicated geological and hydrodynamic conditions. It has to be able to resist super typhoons every year. The tunnel section also has had to cross one of the busiest deep-water passages, the Lingding West Channel, as well as waters that are home to Chinese white dolphins, which are under the State's strict protection.

The bridge has helped set construction standards for other bridges and similar infrastructure projects in coming years, Su said.

The undersea tunnel has been designed and built to ensure large vessels can pass through the busy sea channel. More than 4,000 cargo vessels and ocean liners cross the waters of the Pearl River Estuary every day.

"Due to aviation height limitations, the undersea tunnel is constructed to ensure the safety of planes using Hong Kong International Airport, one of the busiest airports in the world," Su said.

Xu Guoping, a bridge and tunnel expert, said the bridge's undersea tunnel is designed to withstand a magnitude 7 earthquake.