Part of London Bridge station was turned into a makeshift maternity ward when a woman gave birth to a baby boy just before rush hour.
Staff at the busy station scrambled to support a woman who was having contractions on a platform before moving her to a medical room.
The mother, whose name is not known, gave birth to her son shortly after 4.30pm on Thursday.
An image on social media showed Network Rail staff surrounding the new mother, who was pictured wrapped in blankets.
She went into labour on a Southeastern train before being helped onto the platform when it arrived at London Bridge.
Realising the baby was on the way, an announcement was made for doctors and nurses to attend.
Dean Parsons, 43, an information assistant at Southeastern Railway, said: “I work in the control room but was doing work on the platform when a lady came running to my colleague and said there’s a lady on the train which had just pulled in having contractions.
“She collapsed on a bench on the platform.
“We called for the first aid officer from the station and put out an announcement for doctors and nurses.”
The baby boy arrived before paramedics got to the scene, and he was delivered by an off-duty doctor.
Mr Parsons added: “It’s always amazing how quickly doctors and nurses will always respond to announcements. They are fabulous.
“And it was about 3pm, they were just passing and they may have been on their way home from a long shift.
“Luckily with the new station being built we had a medical room. We managed to get her in a wheelchair, I was saying to her ‘try not to push yet.’
“At first the woman was in pain, she had tears in her eyes, the baby was a week early. But the photo taken after shows her beaming.”
A man grabbed a blanket from Oliver Bonas, a homeware store in the station, in an attempt to make the woman as comfortable as possible.
Laura Karklina, who works at the shop, said: “A man ran into our store.
“He explained ‘I need a piece of clothing’. We said okay and just gave him the blanket.”
“We would have given them anything. It was a crazy situation, it’s like one of those once in a lifetime things.”
A post on London Bridge’s Twitter page read: “Our team did a marvellous job helping to deliver a baby boy into the world. Mother and baby doing great.”
A member of staff added: “Great team effort from station staff at London bridge helping the delivery of a baby boy at London bridge today.
“Male staff pacing up and down outside like expectant fathers. Fantastic shift.”