The West-to-East Natural Gas Pipeline crossed the Yellow River, the second largest river system in China, through a tunnel on June 10.

It marks a major breakthrough in the construction of the project, one of the four landmark projects in western China.

The 518-meter-long tunnel was laid 20 meters beneath the bed of Yellow River. It is the first gas pipeline tunnel spanning the Yellow River.

The success of the pipe-laying provided experience for China in large-bore pipelines across large rivers and laid a solid foundation for gas transmission scheduled in the fourth quarter of this year, said a project official.

The pipeline's construction, which will take about six years to complete, began in 2001. In the first stage of the project, the 4,200-kilometer-long pipeline will wind its way through eight autonomous regions and provinces before entering Shanghai.

It is expected to transfer over 12 billion cubic meters of natural gas annually for industrial and domestic use to Shanghai and other Yangtze River Delta areas from gas fields of the Tarim Basin in Xinjiang, home to one of China's largest oil and natural gas reserves with more than 200 billion cubic meters of proven natural gas reserves.