China has opened the world’s longest sea bridge – a 55-kilometre span with a 6.7-kilometre tunnel that will make drivers, and their passengers, feel as if they are plummeting into the sea.

The Hong Kong-Zhuhai-Macau Bridge connects the former British territory to the gambling mecca of Macau, via the mainland China city of Zhuhai.

It will be officially opened on Wednesday, after nine years of construction. The grand ceremony will be attended by Chinese President Xi Jinping and Hong Kong’s leader, chief executive Carrie Lam, among 700 dignitaries.

But the massive building project has not been without scandal. The finished build was delayed by two years, and overran its budget by billions of dollars, eventually costing $28.3 billion.

It has been reported that as many as 10 people died during the construction of the bridge, with another 600 injured.

A 6.7-kilometre tunnel connects two artificial islands. Photo: Getty

The bridge’s main access road to Hong Kong’s port will not be completed until next year, according to The South China Morning Post. In addition, the Dolphin Conservation Society told broadcaster RTHK on Tuesday that construction has led to more than a 40 per cent decline in local populations of the critically endangered Chinese white dolphin, which is a symbol of Hong Kong.

But the bridge will mean residents and visitors to Hong Kong will be able to travel freely to the rest of China. With it, the journey time to Macau, a city popular for its shopping and casinos, will be cut from three hours to just half an hour.

However, private car owners will need a special permit to cross the six-lane bridge. Most people will have to ditch their vehicles and take a $14 shuttle bus or a hire car instead.

Hundreds were injured during the bridge’s construction. Photo: Getty

Anyone hoping to take advantage of the quicker trip will also have to stomach one of the bridge’s most extraordinary features – the 6.7-kilometre undersea tunnel between two artificial islands, designed to prevent disruption to shipping traffic.

Hong Kong’s trading and logistics sector is also expected to be a huge beneficiary.

“Some companies transporting cargo through feeder ships are expected to change their route to the bridge, as it would be much faster,” transport sector spokesman Frankie Yick Chi-ming said.

“Many manufacturers have moved to the west bank of the Pearl River. Their cargo currently has to be transported to Hong Kong via the Humen Bridge [from Guangzhou to Dongguan]. That is a long detour and the congestion at the Humen Bridge can cost us three hours.”

The East Artificial Island, and the entry to the 6.7-kilometre tunnel. Photo: AAP

Steve Tsang, director of London’s China Institute at the School of Oriental and African Studies, said the bridge was part of a larger Chinese investment strategy. It would also bring Hong Kong more into Beijing’s sphere of influence.

“By making Hong Kong an integral part of the Greater Bay area, it will bring Hong Kong closer to mainland China, notwithstanding the official commitment for the ‘one country, two systems’ model,” Professor Tsang said.

“The more Hong Kong is integrated into mainland China, the less is there a case for it to be given very special treatment.”

Hong Kong residents have also expressed concerns about the costly new structure. Many believe it will not benefit the city, which has suffered a massive rise in housing costs and homelessness in recent years.

“It links Hong Kong to China almost like an umbilical cord. You see it, and you know you’re linked up to the motherland”, one source told CNN.

Environmental groups raised concerns over the project’s effect on the white dolphin population. Photo: Getty

-with agencies