Staff members renew the air conditioner filter of a bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush. (Photos: Xinhua)

A maintenance worker checks a bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A staff member disinfects air conditioner filters of the bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A maintenance worker works at a bullet train maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

Aerial photo taken on Jan. 28, 2021 shows bullet trains to be maintained at a maintenance base in Zhengzhou, central China's Henan Province. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

Aerial photo taken on Jan. 28, 2021 shows bullet trains to be maintained at a maintenance base in Zhengzhou, central China's Henan Province. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

Aerial photo taken on Jan. 28, 2021 shows bullet trains to be maintained at a maintenance base in Zhengzhou, central China's Henan Province. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A staff member disinfects the train car of a bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A staff member renews the air conditioner filters of the bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A maintenance worker works at a bullet train maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A staff member disinfects the train car of a bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

Staff members conduct maintenance work for a bullet train with a robot check at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A maintenance worker checks a bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.

A staff member disinfects the air conditioner filter of a bullet train at a maintenance base in Zhengzhou, central China's Henan Province, Jan. 28, 2021. Zhengzhou section of China Railway Zhengzhou Bureau Group Co., Ltd. carries out maintenance work and epidemic precaution for trains to prepare for the country's annual Spring Festival travel rush.