The Estonian government again aired its concerns over plans to build the world’s largest undersea rail tunnel that would connect the cities of Tallinn and Helsinki.

Minister of Public Administration Jaak Aab on Friday met with the tunnel’s developer, Finest Bay Area Development Oy, as well as China Railway International Group, Touchstone Capital Partners Ltd. and companies involved in the project’s design.

While Estonia “supports the idea of a Tallinn-Helsinki tunnel that would be connected to the future Rail Baltic railway,” doubts linger over the estimated passenger and freight numbers, the government said. In addition, the project’s tight timetable is “not feasible,” Aab said.

The tunnel between the Finnish and Estonian capitals would span more than 100 kilometers (62 miles) and entails construction of at least one artificial island. The project’s founder, Peter Vesterbacka, has said he aims to open the tunnel in 2024. Touchstone Capital has agreed to provide 15 billion euros ($17 billion) in funds for the project.

“An undersea tunnel between Finland and Estonia can only be constructed in cooperation with both governments,” the Estonian government said.