The presentation included representatives of design and research institutions from Shanghai, spokespeople for Tallinn City Government said.

Vesterbacka's goal is to build the tunnel using private sector funding. According to his project, construction of the €15 billion tunnel could begin in the next couple of years already.

Riisalu said that the good news about the project was that the plan presented by Vesterbacka and his partners was in no way connected to the arrival of the Rail Baltic railway project.

"This is a fully independent project based on private capital, investors and the best global engineering know-how," Riisalu said. "What makes this project attractive is that, if there is interest in it, it could be launched much earlier, and its aim would be to merge two Nordic cities into a twin city, which has been previously discussed a great deal as well. The tunnel would transform Tallinn and Helsinki into a single business and cultural area, and would attract new investments."

Izmailova said that, as a vision, a twin city has captured the minds of the residents of Tallinn and Helsinki for years already.

She noted that of all tunnel projects, the one presented by Vesterbacka is the most acceptable to her as someone upholding a green worldview. "That the tunnel can be build and will also be feasible without the new Rail Baltic track which will split the Estonian territory is positive news overall," said the deputy mayor.

A project called FinEst Link has also been launched by various Estonian and Finnish national institutions and the two capital cities to conduct cost-benefit studies for a tunnel project which would become part of the Trans-European Transport Network (TEN-T) in combination with the planned Rail Baltic high-speed railway.

The official preliminary study being funded by the EU is due to be completed by next February, which would allow construction on the tunnel to begin in the 2030s. The FinEst Link project currently involves the cities of Helsinki and Tallinn, Uusimaa Region, Harju County as well as the states themselves of Finland and Estonia.