A worker from China Railway Seventh Group Co., Ltd. works at the construction site of a project in Weiyang District of Xi'an City, capital of northwest China's Shaanxi Province, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Liu Xiao)

A worker from China Railway Seventh Group Co., Ltd. works at the construction site of a railway station of Xi'an Subway Line 8 in Xi'an City, capital of northwest China's Shaanxi Province, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Liu Xiao)

Workers are busy at the construction site of a smart factory in the economic and technological development zone in Yinchuan City, northwest China's Ningxia Hui Autonomous Region, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Feng Kaihua)

A worker from China Railway Seventh Group Co., Ltd. works at the construction site of a project in Weiyang District of Xi'an City, capital of northwest China's Shaanxi Province, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Liu Xiao)

A worker is busy at the construction site of a smart factory in the economic and technological development zone in Yinchuan City, northwest China's Ningxia Hui Autonomous Region, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Feng Kaihua)

Workers lay tracks at the construction site of a section of the China-Laos Railway project in Xishuangbanna Dai Autonomous Prefecture, southwest China's Yunnan Province, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Photo by Li Yunsheng/Xinhua)

Workers are busy at the construction site of a project in the economic and technological development zone in Yinchuan City, northwest China's Ningxia Hui Autonomous Region, May 1, 2021. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Feng Kaihua)