Checkpoint staff members check the passes of the foreign crew of a ship in the entry procedures in Qinhuangdao, north China's Hebei Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Yang Shiyao)

A worker is seen at a construction site of the Panda House in a wild zoo in Xining, northwest China's Qinghai Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Hongxiang)

A worker is seen at a construction site of the Panda House in a wildlife park in Xining, northwest China's Qinghai Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Hongxiang)

A nurse cares for a patient in an emergency ward in the hospital of Ningxia Medical University in northwest China's Ningxia Hui Autonomous Region, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Feng Kaihua)

A worker is seen at a construction site of the Panda House in a wildlife park in Xining, northwest China's Qinghai Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Hongxiang)

Medical workers of emergency department work in the hospital of Ningxia Medical University in northwest China's Ningxia Hui Autonomous Region, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Feng Kaihua)

Checkpoint staff members deal with entry procedures for foreign crew of a ship in Qinhuangdao, north China's Hebei Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Yang Shiyao)

Medical workers of emergency department work in the hospital of Ningxia Medical University in northwest China's Ningxia Hui Autonomous Region, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Feng Kaihua)

Workers of the China Railway No. 18 Engineering Group are seen at a construction site in Kunming, southwest China's Yunnan Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Yang Zongyou)

A worker of China Construction Third Engineering Division Co., Ltd. is seen at a construction site in Xi'an, northwest China's Shaanxi Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Bowen)

Workers of the China Railway No. 18 Engineering Group are seen at a construction site in Kunming, southwest China's Yunnan Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Yang Zongyou)

Workers of the China Railway No. 18 Engineering Group are seen at a construction site in Kunming, southwest China's Yunnan Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Yang Zongyou)

A worker of China Construction Third Engineering Division Co., Ltd. is seen at a construction site in Xi'an, northwest China's Shaanxi Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Bowen)

Workers of China Construction Third Engineering Division Co., Ltd. are seen at a construction site in Xi'an, northwest China's Shaanxi Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Bowen)

A farmer catches crayfish at a mixed farm in Huanglu Town of Chaohu City, east China's Anhui Province, May 1, 2019. People from various sectors stick to their posts during the Labor Day holiday. (Xinhua/Zhang Duan)