[InKunming--Sister Cities] Photo taken on April 12, 2019 show the construction site of the Pu'er railway station of the China-Laos railway in Pu'er City, southwest China's Yunnan Province,. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

A worker directs a road roller at the construction site of the Pu'er railway station of the China-Laos railway in Pu'er City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

Workers remove slag in the Xinping tunnel of the China-Laos railway in Yuxi City, southwest China's Yunnan Province, April 11, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

The Monei River bridge of the China-Laos railway is under construction in Pu'er City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

The Ganlanba bridge of the China-Laos railway is under construction in Jinghong City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

A worker fastens a screw at the construction site of the Monei River bridge of the China-Laos railway in Pu'er City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

Worker Wu Yuanbo (R) and colleagues test the compaction degree of the roadbed of the under-construction Pu'er railway station of the China-Laos railway in Pu'er City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

The Ganlanba bridge of the China-Laos railway is under construction in Jinghong City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

Workers Zhong Qi (L) and Feng Zhuang examine the Monei River bridge of the China-Laos railway in Pu'er City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)

Laborers work at the construction site of the Monei River bridge of the China-Laos railway in Pu'er City, southwest China's Yunnan Province, April 12, 2019. Linking Yuxi City in Yunnan and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational by the end of 2021. (Xinhua/Qin Qing)