Workers conduct power-supply installation at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Zhu Xiang)

Workers conduct power-supply installation at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Zhu Xiang)

Workers conduct power-supply installation at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Hao Yuan)

Workers conduct power-supply installation at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Hao Yuan)

A worker works at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Zhu Xiang)

Workers conduct power-supply installation at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Zhu Xiang)

Workers conduct power-supply installation at the construction site of the subway line 4 in Zhengzhou, central China's Henan Province, April 24, 2020. The 30 km subway line is now under construction here. (Xinhua/Zhu Xiang)