A construction machine pushes out the long steel rail of the Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. The Lhasa-Nyingchi railway will help improve the railway network as well as transportation infrastructure along the railway, pushing forward the economic and social development in the region. (Xinhua/Li Xin)

Workers lay the long steel rail inside a tunnel of the Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Li Xin)

The construction site of track-laying is seen inside a tunnel of the Lhasa-Nyingchi railway in Gonggar County of Shannan City, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Chogo)

The long steel rail is seen for laying tracks of the Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Chogo)

Workers lay the long steel rail for the Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Li Xin)

Workers prepare for laying the long steel rail for Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Li Xin)

Workers lay the long steel rail for the Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Chogo)

Workers place screws before laying tracks for the Lhasa-Nyingchi railway in Gonggar County of Shannan Prefecture, southwest China's Tibet Autonomous Region, March 8, 2019. The first 500-meter-long steel rail was successfully laid on the ballastless tracks of the Lhasa-Nyingchi Railway on Friday. (Xinhua/Chogo)