Workers reinforce tracks in the rain near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Hou Deqiang)

Workers reinforce tracks in the rain near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Hou Deqiang)

A worker maintains rails before rainfall near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Zhang Hongxiang)

Workers reinforce tracks near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Zhang Hongxiang)

Workers maintain rails near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Zhang Hongxiang)

A worker checks the condition of rails near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Zhang Hongxiang)

A worker checks the condition of rails near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Zhang Hongxiang)

Workers reinforce tracks near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Zhang Hongxiang)

A worker maintains rails near the Tanggula Station of the Qinghai-Tibet railway, northwest China's Qinghai Province, June 30, 2018. Maintenance workers stick to their posts everyday to guarantee the operation of the Qinghai-Tibet railway at the Tanggula Station with an altitude of 5,072 meters above sea level. The 1,956-kilometer-long railway, which began service in July 2006, is the world's highest plateau railroad connecting Xining in Qinghai and Lhasa in Tibet Autonomous Region. (Xinhua/Hou Deqiang)