Gansu's Dongshan tunnel at average altitude of 3,850 meters drilled through

Workers of the China Railway No.4 Engineering Group celebrate the drill-through of the Dongshan tunnel along the national highway No. 213 in Yugur Autonomous County of Sunan of northwest China's Gansu Province, on March 2, 2021. The 3,639-meter Dongshan tunnel at an average altitude of 3,850 meters was drilled through on Tuesday. It is a critical project for national highway No. 213 that connects Sunan to Qilian County in Qinghai Province, also in northwest China. (Xinhua/Chen Bin)