The DKr 22.2bn ($US 3.4bn) Cityringen is due to open in July 2019, linking Copenhagen Central with the city centre and the districts of Østerbro, Nørrebro, Vesterbro, and Frederiksberg. The 15.5km line runs underground for its entire length and will have 17 stations, constructed at depths of up to 35m. Two branches are also planned which will extend metro services to Sydhavn and Nordhavn.

Civil works on the Cityringen are being carried out by the Copenhagen Metro Team consortium of Salini-Impreglio, Seli, and Tecnimont.

With the opening of the Cityringen, Copenhagen Central is expected to become Denmark's busiest station, taking the title currently held by nearby Norreport. The total number of passengers using the station is expected to increase from 40 million to 88 million per year or 285,000 passengers per day, with around 90,000 passengers per day expected to pass through the metro station.

The metro station will be linked to the existing station by a tunnel beneath Reventlowsgade, which will join the existing subway linking the main line and S-Train platforms.

"For a lot of passengers Cityringen means fewer changes and an easier life," says Heunicke. "And in the end it means more people will use public transport."

The opening of the Cityringen is expected to double metro ridership to 130,000 passengers per day by 2025.