Source: Highways Department Hong Kong

Nine years in the making, the world's longest sea bridge, connecting Hong Kong, Macau and mainland China, made its debut this week thanks to a preview offered by the Chinese government.

At 34 miles long (55 kilometers), construction of the bridge began nine years ago and includes winding roads and an underwater tunnel, which, according to Gao Xinglin, the bridge's project planning engineer, led to many a sleepless night for him.

"There were many nights where I couldn't fall asleep, because there were too many difficulties during the construction," Gao told reporters Wednesday.

"Linking the 80,000-tonne pipes under the sea with watertight technology was the most challenging," he added.

Expected to cut travel time by 60 percent when completed, the bridge has cost an estimated $15.1 billion (100 billion yuan) so far, with enough steel to construct 60 Eiffel Towers and features including artificial islands, linked roads and new border crossing facilities.

However, delays, budget overruns, accusations of corruption and the deaths of a few construction workers have prevented the bridge from opening. As such, no official opening date has been set.