The developers of the world's longest undersea railway tunnel, which will connect the Finnish and Estonian capitals, have reached an agreement for a €15 billion (Dh61.89bn) funding. The financing, which will be provided by China's Touchstone Capital Partners, will cover the cost of the project, the tunnel company Finest Bay Area Development Oy said on Friday. A third of the funding will be made in the form of a private equity investment, giving Touchstone a minority stake, and two-thirds are debt financing, according to the preliminary agreement. The planned tunnel between Helsinki and Tallinn will span more than 100 kilometres and entails the construction of at least one artificial island. "Financial details will be negotiated over the next six months," FinEst Bay Area said It had earlier estimated the total cost of the tunnel at €15bn to €20bn, reported Bloomberg. The company raised the first external funding of €100 million from the Dubai construction company ARJ Holding in December, and is seeking European investors to join. "Now, the financing is sorted and we can move ahead," project leader Peter Vesterbacka, a former executive at the Angry Birds game maker Rovio, told Reuters. The governments of Finland and Estonia have said they will work toward securing European Union funding for the tunnel, which could reduce the amount of private funding needed. Touchstone’s financing is available to Finest Bay Area Development in tranches as the project progresses, with financial details of the contract set to be negotiated over the next six months. It is not clear from the press release whether Touchstone has raised the money, or committed to doing so.