The 1,500km eastern section of the west-east pipeline officially began supplying natural gas to Shanghai.
The multi-billion US dollar link will eventually stretch 4,000km to Xinjiang on completion in 2005.
Royal/Dutch Shell, Russia's Gazprom and Exxon Mobil of the US all hold stakes in the project. Overseas-listed PetroChina and refiner Sinopec hold the rest.
Coal currently accounts for about 70% of China's energy needs and natural gas only 2% but the government hopes to lift the natural gas proportion to between 7 and 8% by 2010 in order to reduce air pollution.