ZHUHAI, China — China on Tuesday opened the world’s longest sea-crossing bridge linking Hong Kong to the mainland, a feat of engineering carrying immense economic and political significance.

Chinese President Xi Jinping presided over a ceremony in the city of Zhuhai to open the 55-kilometer (34-mile)-long bridge linking it to the semi-autonomous regions of Hong Kong and Macau. Digital fireworks exploded on a screen behind him as leaders of the three cities watched.

The $20 billion bridge took almost a decade to build while incurring major delays and cost overruns. It includes an undersea tunnel allowing ships to pass through the Pearl River delta, the heart of China’s crucial manufacturing sector.

Its opening will cut travel time across the delta from several hours to just 30 minutes, something China hopes will bind the region together as a major driver of future economic growth. Heavily regulated traffic using permits issued under a quota system will begin flowing on Wednesday.

The bridge forms a physical link between the mainland and Hong Kong, an Asian financial hub that was handed over from British to Chinese control in 1997 with the assurance it would maintain its own legal and economic system for 50 years.

That carries major political significance for Xi’s administration, which has rejected calls for political liberalization 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.

The bridge’s opening also comes a month after the inauguration of a new high-speed rail link from Hong Kong to mainland China that runs along a different, shorter route. That line has vastly decreased travel times but also raised concerns about Beijing’s growing influence because mainland Chinese law applies within part of the line’s Hong Kong terminus.

To Claudia Mo, a Hong Kong democratic politician, the bridge’s political significance outweighs its practical usefulness.

“It’s not exactly necessary, because Hong Kong is connected to mainland China in every way already, by land, by air, by sea,” Mo told The Associated Press.

“But they still need it as a political symbol or icon to remind Hong Kong people … that you are connected to the motherland, with this very grand bridge. It’s almost like an umbilical cord.”