Opened in 1972, the 1.86-kilometre Cross Harbour Tunnel is the first tunnel built under water in Hong Kong, providing a physical road link between Kowloon and Hong Kong Island. It was the longest tunnel of its type at the time, and still the city's most busy tunnel with an average daily vehicular flow of above a hundred thousand to date.

The project involved the construction of a set of twin steel tubes supported with reinforced concrete.