The bridge is made of 420,000 tons of steel - enough to build 60 Eiffel Towers.
The extraordinary design also includes a 6.7km (4mile) submerged tunnel to help it avoid the busy shipping paths over the Pearl River Delta.
Residents of Hong Kong react to the opening of the world's longest sea-crossing bridge. The construction of the bridge has dragged on for almost a decade - authorities started building in 2009 - and it has been plagued by problems, including suspicions that parts of the bridge were floating away.
Mind you, that's not to say the bridge has been without controversy, amid many delays, overrunning budgets, corruption prosecutions and even the deaths of some construction workers.
An evening view of the Hong Kong-Zhuhai-Macau bridge and its entrances to a cross sea tunnel, off Lantau island in Hong Kong, China October 21, 2018, before its opening ceremony on October 23, 2018.
It is part of China's plan to create a Greater Bay Area, including Hong Kong, Macau and nine other cities in southern China.
Because Macau and Hong Kong are semi-autonomous regions with a degree of independence from mainland China, some people are suspicious that the bridge could be used to increase Beijing's control across the territories.
That carries major political significance for Mr Xi's administration, which has rejected calls for political liberalisation in Hong Kong, sparking fears Beijing will clamp down further on civil liberties before the end of the "one country, two systems" arrangement in 2047. It will open to regular traffic on Wednesday.
But officials say the bridge will cut journey times between the cities from three hours to just 30 minutes and will be in use for 120 years. It's also been described as one of the world's most unusual roadways, reportedly boasting special features like yawn-detecting cameras and blood pressure-monitoring machines.
"It links Hong Kong to China nearly like an umbilical cord". Instead, a majority of traffic will come from shuttle buses or "special hire cars". Others raised environmental concerns over the Chinese white dolphins that frequent the area, as well as other objections.
The bridge's opening comes at a challenging time for China as it faces pressure from a trade war with the United States, volatile financial markets, mounting public debt and a slowing economy.
"I am not so sure either how the bridge can sustain itself if not many cars are using it", Tanya Chan told BBC News Chinese.