Feng Shuai marks the date on a checked train part. [Photo by Liu Wei/chinadaily.com.cn]

Every day Beijing south train depot starts getting busy at dusk when work is winding down in other places.

Beijing south train depot is a '4s service station' for bullet trains.

It is 10 kilometers from Beijing South Railway Station and where more than 3,000 people work in the 1,800 square meter factory.

"Usually the trains go out during daytime and come back here for maintenance at night," said a staff member.

The station has the most tracks as any service shop across the nation with 12 able to handle 24 trains with eight carriages each.

Feng Shuai, a 25-year-old primary repair worker, was checking the side of a bullet carriage inch by inch and kept knocking on the body to see if was intact.

"Usually we check the trains' appearance in case it's broken and replace the worn-out parts," said Feng, "I can say our work can score 100 out of 100 since we think of passengers' safety all the time and do a great job."

After one part has been checked, Feng takes out a piece of chalk and marks the date.

"I knock more than one thousand times during one day at work and my knucklebone gets swollen," Feng said.

The repairers spend about 16 hours a day on average checking the trains and become busier during Spring Festival.

Wang Jian, workshop chief on duty, said: "All workers canceled the Spring Festival holiday to guarantee all the trains can be checked on time and well maintained."