The North European Gas Pipeline, a product of a partnership between Germany and Russia, will connect to existing lines from gas fields in western Siberia, creating an even longer 3000km structure.
The pipeline will primarily serve Germany, with branch-lines to Scandinavia, the Netherlands and the UK.
The $US4.7 billion dollar pipeline will have the capacity to produce 27.5 billion cubic metres of gas a year, with provision for a parallel pipeline that would increase capacity to 55 billion cubic metres.
Construction costs are being shared by the Russian state-controlled gas company Gazprom and Germany's E.ON-Ruhrgas and Wintershall.
The pipeline will run under the Baltic Sea, bypassing countries including Belarus, Ukraine and Poland.
Authorities said the offshore route, which added $US2.4 billion to construction costs, would eliminate transit fees and the risk of the supply being cut if disputes arose.
