Russia launched construction Monday of a 770 billion ruble ($20.8 bn) gas pipeline that will help bring gas from the far east of the country to China.

"We are today starting the biggest construction project in the world," President Vladimir Putin said at the ceremonial joining of the first sections of the 3,968-kilometre (2,466-mile) Siberian Strength pipeline outside the eastern Siberian city of Yakutsk.

"But it is not about records, it is the fact that it is an extremely important project for the Russian Federation and for the People's Republic of China," he said, according to comments broadcast on national TV.

China's Vice Premier Zhang Gaoli, who was also in attendance at the ceremony, said he hoped the pipeline would be completed within four years.

"China already plans in the first half of next year to start building the Chinese section of the pipeline and we should make an effort to complete construction and begin exploitation of the pipeline in 2018," he said.

In May the two countries signed a 30-year deal which will eventually see Russia supplying China with 38 billion cubic metres of gas per year, an agreement worth some $400 billion.

The pipeline, which will have a total capacity of 61 billion cubic metres per year, will also link the gas fields in Yakustsk and Irkustsk to cities across the Russian far east.

Putin said earlier that the project would allow for increased hydrocarbon exports and was "also a major step forward in the gasification of our own country."

Russia is the top gas exporter in the world, but to date most exports have gone to Europe.