Staff members celebrate the completion of Altun Mountains Tunnel on the Golmud-Korla railway line, connecting Golmud in Qinghai Province and Korla in Xinjiang Uygur Autonomous Region, on Nov. 19, 2019. After three and half years of construction work, the Altun Mountains Tunnel was dug through Tuesday. (Xinhua/Song Yanhua)

Photo taken on Nov. 19, 2019 shows the Altun Mountains Tunnel on the Golmud-Korla railway line, connecting Golmud in Qinghai Province and Korla in Xinjiang Uygur Autonomous Region, on Nov. 19, 2019. After three and half years of construction work, the Altun Mountains Tunnel was dug through Tuesday. (Xinhua/Song Yanhua)