Beijing Friday started work on an underground water diversion tunnel to help bring water from the country's south to the thirsty national capital.

The tunnel will be about 44.7 km long and involves an estimated investment of 9.17 billion yuan (1.4 billion U.S. dollars), said He Fengci, a deputy director of the general office of the Beijing Construction Committee of the South-to-North Water Diversion project.

The tunnel will supply water to the downtown area and two suburban areas in the southeast, He said. Local water sources have been unable to meet fast growing demand.

One billion cubic meters of water will be diverted from the Yangtze River, the country's largest, to Beijing annually through the middle route of the South-to-North Water Diversion Project after the flood season in 2014, the official said.

The South-to-North Water Diversion Project is designed to divert water from the water-rich south of China, mainly the Yangtze, to the country's arid northern regions.

Over the next few years, Beijing will also finish building 21 other affiliated diversion projects, water conservation projects and water plants.