The 1,220-kilometre Nord Stream pipeline is the first direct link between western Europe and Russia, which provides for around quarter of the EU’s gas supplies.
The pipeline will deliver enough energy to supply 26m households across Europe when it is fully completed next year.
The launch yesterday saw the pipeline filled with so-called buffer gas, which helps create the right level of pressure before it is ready to start transporting gas to Europe in about a month’s time.
Speaking at the event in the northern city of Vyborg, Russian prime minister Vladimir Putin said the Nord Stream project would reduce Russia’s dependence on Ukrainian pipelines and ease relations between the two neighbouring countries.
Ukraine has been locked in disputes with Russia over gas prices and debt for more than a decade.
A stand-off between the two countries in 2009 choked gas supplies to parts of Europe in the dead of winter, putting pressure on Gazprom to develop routes avoiding conflict areas.
Ukraine, which has told Russia it wants to renegotiate the gas agreement to secure lower prices and import less gas, has said that if the two sides cannot reach agreement it will seek arbitration in Stockholm.
The $12.5bn Nord Stream project, agreed in 2005 by then German chancellor Gerhard Schroeder and Russia’s Putin, is made up of two pipelines and should be able to move 55bn cubic metres of gas a year by 2013, after the completion of the second pipeline.
State-owned Gazprom owns 51 per cent of Nord Stream, the company building the pipeline, alongside Germany’s Wintershall, E.ON Ruhrgas, the Dutch company NV Nederlandse Gasunie and France’s GDF Suez.
Gazprom is also leading the South Stream pipeline project, which will run from southern Russia to Bulgaria under the Black Sea.