LHASA -- Construction of a highway passing through the Yarlung Zangbo Grand Canyon, known as the world's deepest canyon with a maximum depth of 6,009 meters, was completed on Saturday in Southwest China's Tibet autonomous region.

The project took almost seven years to complete.

A 2,114-meter tunnel was dug through on Saturday morning, marking the completion of the major construction of the 67.22-km road connecting Pad Township in the city of Nyingchi and Medog County.

The project was built by the China Huaneng Group Co Ltd and started in 2014, with an estimated investment of over 2 billion yuan (about $310 million).

The company stressed green development during the construction and poured 110 million yuan into ecological and water environment protection. It was much more than the planned 75.39 million yuan, said Du Canxun, a manager with the company.

The road was built on the former hiking route between Nyingchi's Pad township and Baibung township, Medog county, with an altitude difference of up to 2,892 meters between the highest and lowest spots of the road.

It is the second significant passageway to Medog, following the first one connecting the county and Zhamog township, Bomi county. After the new highway opens to traffic, the road length connecting the city proper of Nyingchi and Medog county will be shortened to 180 km from 346 km, cutting travel time by eight hours.