With ambitions to see an additional 250 million people move into China’s cities in the next decade, the country has become known for ‘mega projects’ – mind boggling feats of engineering created to keep pace with a growing population. 

The latest of these is the world’s largest sea bridge, connecting mainland China with Hong Kong and Macau.

After eight years of construction, the 55 kilometre, AUD $19 billion Hong Kong-Zhuhai-Macau Bridge will soon be open to traffic.  

The challenges that faced the project’s engineers were immense – the soft and sometimes deep seabed the bridge rests on has resulted in 100 massive steel cylinders being driven into the sandy bottom to form the foundations for two artificial islands. The project was reportedly built using more steel than Eiffel Towers – a staggering 380,000 tonnes.

In addition, engineers were forced to contend with height restrictions, as a result of being in the Hong Kong International Airport’s flightpath, and the need to allow the unrestricted passage of a huge number of ships – solved by building a 6 kilometre undersea tunnel.

The bridge has also been designed to withstand earthquakes and seasonal typhoons.

An estimated 40,000 vehicles per day are expected to use the bridge, which will cut travel time between in half, allowing commuters to make the journey across the Pearl River Estuary from Macau to Hong Kong in about an hour.

About 14,000 workers and 300 ships worked on the bridge at the peak of its construction.

"We have included a lot of foreign experts from the UK, US, Denmark, Switzerland, Japan, and the Netherlands," Gao Xinglin, Bridge team leader, told Al Jazeera. "They are from around 14 countries."

However, the challenges haven’t purely been engineering-based; the bridge is a source of political sensitivity, given that Hong Kong maintains a separate, more liberal legal system.