Aerial photo taken on May 20, 2020 shows the construction site of Tianshan Shengli tunnel in northwest China's Xinjiang Uygur Autonomous Region. Tianshan Shengli tunnel, a six-year project on the Urumqi-Yuli highway, passes through a cold and high altitude zone, with harsh climate and geological condition. (Xinhua/Hu Huhu)

Machinery lay concrete at the construction site of Tianshan Shengli tunnel in northwest China's Xinjiang Uygur Autonomous Region, May 19, 2020. Tianshan Shengli tunnel, a six-year project on the Urumqi-Yuli highway, passes through a cold and high altitude zone, with harsh climate and geological condition. (Xinhua/Hu Huhu)

Workers work at the construction site of Tianshan Shengli tunnel in northwest China's Xinjiang Uygur Autonomous Region, May 19, 2020. Tianshan Shengli tunnel, a six-year project on the Urumqi-Yuli highway, passes through a cold and high altitude zone, with harsh climate and geological condition. (Xinhua/Hu Huhu)

A worker binds steel bars at the construction site of Tianshan Shengli tunnel in northwest China's Xinjiang Uygur Autonomous Region, May 19, 2020. Tianshan Shengli tunnel, a six-year project on the Urumqi-Yuli highway, passes through a cold and high altitude zone, with harsh climate and geological condition. (Xinhua/Hu Huhu)

Photo taken on May 19, 2020 shows the construction site of Tianshan Shengli tunnel in northwest China's Xinjiang Uygur Autonomous Region. Tianshan Shengli tunnel, a six-year project on the Urumqi-Yuli highway, passes through a cold and high altitude zone, with harsh climate and geological condition. (Xinhua/Hu Huhu)

Photo taken on May 19, 2020 shows the construction site of Tianshan Shengli tunnel in northwest China's Xinjiang Uygur Autonomous Region. Tianshan Shengli tunnel, a six-year project on the Urumqi-Yuli highway, passes through a cold and high altitude zone, with harsh climate and geological condition. (Xinhua/Hu Huhu)