XI'AN, July 16 -- China has dug through a mountain range to supply water from a tributary of the country's longest river Yangtze to quench the droughty north.

Tunnels beneath the Qinling Mountains on Sunday started sending water from the Hanjiang River, the largest tributary of the Yangtze, to the Weihe River, a tributary of the Yellow River, said the water resources department of Shaanxi Province.

Officials hailed the project for allowing water from tributaries of the country's two largest rivers to meet in Shaanxi, one of the most drought-ridden provinces in northwest China.

Involving total investments of 51.6 billion yuan (7.2 billion U.S. dollars), the project started construction in 2011 to bring water from Hanjiang in water-rich southern Shaanxi northward to Weihe, which traverses the more thirsty central parts of the province.

It is one of the most challenging engineering projects in China as it requires constructing 98.3-km tunnels underneath the Qinling Mountains, a natural boundary between China's north and south.

So far, the project has completed the first phase to link the two rivers through tunnels, while the second and third phases of sending water to other places in central Shaanxi are still under construction.

After the entire project is completed, it will relieve water supply strains in Shaanxi cities such as Xi'an and Xianyang, benefiting 14.11 million people. It will also spare more water resources for northern Shaanxi to develop its energy industry, said Zheng Weiguo, director of the provincial water resources department.

"This project has far-reaching significance. It will quench northern Shaanxi, nourish central Shaanxi, and boost green development of southern Shaanxi," Zheng said, adding the project will also allow southern Shaanxi to harness local water resources for green development.