The third phase of a project to carry natural gas from western areas to the east started construction on Tuesday, in a bid to increase imported clean energy to meet China's growing demand.

The project's designed annual capacity is 30 billion cubic meters. It will help to increase imported natural gas every year from Central Asia to 25 billion cubic meters, and it will deliver 5 billion cubic meters of coal gas from the Xinjiang Uygur autonomous region to central and eastern parts of China.

The project, which has a total investment of 125 billion yuan ($20 billion), includes a main line, eight branch lines, three gas storage facilities and a liquid natural gas station. Its total length is 7,378 kilometers, and it covers 10 provinces and autonomous regions.

"The completion of the project will help millions of people in the provinces along the lines to start using clean energy," Vice-Premier Li Keqiang said in a letter. "It will also improve China's energy structure and contribute to the country's target of reducing carbon emissions."

The project will also bring business opportunities to related industries such as equipment manufacturing, Li said.

The project will be able deliver 30 billion cubic meters of natural gas to the market every year, which will help to raise the percentage of natural gas consumption in the country's energy mix from the current 4.6 percent to 5.6 percent, said Liu Tienan, head of the National Energy Administration.

The three main suppliers of natural gas delivered by the line will be Turkmenistan, Uzbekistan and Kazakhstan. Xinjiang will also supply coal gas. The project is expected to be completed by 2015.