Workers of China Railway No. 5 Engineering Group (CREC-5) use ice blocks to cool off at the China-Laos railway Ban Konlouang Tunnel construction site in the Namor District of Oudomxay Province, Laos, Aug. 1, 2019. Rainy season in the Namor District of Oudomxay Province, some 400 km north of the Lao capital Vientiane, is relatively cool in late July, while at the Ban Konlouang Tunnel construction site, located inside mountains there, Chinese workers are sweating. The 9,020-meter Ban Konlouang Tunnel is the second longest tunnel along the China-Laos railway in northern Laos, which is constructed by China Railway No. 5 Engineering Group. (CREC-5/Handout via Xinhua)

Workers of China Railway No. 5 Engineering Group (CREC-5) carry ice blocks to cool down the China-Laos railway Ban Konlouang Tunnel construction site in the Namor District of Oudomxay Province, Laos, Aug. 1, 2019. Rainy season in the Namor District of Oudomxay Province, some 400 km north of the Lao capital Vientiane, is relatively cool in late July, while at the Ban Konlouang Tunnel construction site, located inside mountains there, Chinese workers are sweating. The 9,020-meter Ban Konlouang Tunnel is the second longest tunnel along the China-Laos railway in northern Laos, which is constructed by China Railway No. 5 Engineering Group. (CREC-5/Handout via Xinhua)

A worker of China Railway No. 5 Engineering Group (CREC-5) drinks water at the China-Laos railway Ban Konlouang Tunnel construction site in the Namor District of Oudomxay Province, Laos, July 30, 2019. Rainy season in the Namor District of Oudomxay Province, some 400 km north of the Lao capital Vientiane, is relatively cool in late July, while at the Ban Konlouang Tunnel construction site, located inside mountains there, Chinese workers are sweating. The 9,020-meter Ban Konlouang Tunnel is the second longest tunnel along the China-Laos railway in northern Laos, which is constructed by China Railway No. 5 Engineering Group. (CREC-5/Handout via Xinhua)

An engineer of China Railway No. 5 Engineering Group (CREC-5) works at the China-Laos railway Ban Konlouang Tunnel construction site in the Namor District of Oudomxay Province, Laos, Aug. 5, 2019. Rainy season in the Namor District of Oudomxay Province, some 400 km north of the Lao capital Vientiane, is relatively cool in late July, while at the Ban Konlouang Tunnel construction site, located inside mountains there, Chinese workers are sweating. The 9,020-meter Ban Konlouang Tunnel is the second longest tunnel along the China-Laos railway in northern Laos, which is constructed by China Railway No. 5 Engineering Group. (CREC-5/Handout via Xinhua)

Workers of China Railway No. 5 Engineering Group (CREC-5) carry ice blocks to cool down the China-Laos railway Ban Konlouang Tunnel construction site in the Namor District of Oudomxay Province, Laos, July 30, 2019. Rainy season in the Namor District of Oudomxay Province, some 400 km north of the Lao capital Vientiane, is relatively cool in late July, while at the Ban Konlouang Tunnel construction site, located inside mountains there, Chinese workers are sweating. The 9,020-meter Ban Konlouang Tunnel is the second longest tunnel along the China-Laos railway in northern Laos, which is constructed by China Railway No. 5 Engineering Group. (CREC-5/Handout via Xinhua)