Tourists visit the Mogao Caves in Dunhuang, northwest China's Gansu Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Fan Peishen)

Tourists visit Beijing International Horticultural Exhibition in Beijing, capital of China on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Zhang Chenlin)

Tourists visit the West Lake in Hangzhou, east China's Zhejiang Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Huang Zongzhi)

Tourists visit the West Lake in Hangzhou, east China's Zhejiang Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Huang Zongzhi)

Tourists visit an aquarium in Shenyang, northeast China's Liaoning Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Long Lei)

Tourists visit an aquarium in Shenyang, northeast China's Liaoning Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Long Lei)

Tourists visit Beijing International Horticultural Exhibition in Beijing, capital of China on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Zhang Chenlin)

Tourists visit the Mogao Caves in Dunhuang, northwest China's Gansu Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Fan Peishen)

Tourists visit Beijing International Horticultural Exhibition in Beijing, capital of China on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Zhang Chenlin)

Tourists visit the West Lake in Hangzhou, east China's Zhejiang Province on May 1, 2019, the first day of the four-day May Day holiday. (Xinhua/Huang Zongzhi)