A London Underground service pulled away with a baby on board as the mother stood "distraught" on the platform.
The woman, in her late 20s, had pushed her child's pram on board as the doors closed, and did not manage to board the Circle Line service.
Passengers pulled the emergency cord but the train, after briefly stopping, carried on to Gloucester Road.
Transport for London said the mother was escorted to Gloucester Road to be reunited with her baby.
Passenger Malcolm Dyer, 59, from Ascot, who helped to look after the baby, said: "She pushed the pram on and all of a sudden the doors shut on to her hands, so she naturally let go and left the baby on there and the train started moving.
"I shouted at someone to pull the alarm, which they did and the train stopped momentarily. The baby was merrily sleeping, unaware of anything that had happened."
Staff from South Kensington phoned ahead to the next station, Gloucester Road, and Mr Dyer and a couple on holiday took the baby off the train.
Mr Dyer said: "She was a bit silly trying to put a pram and herself on the train when the beeps were indicating the doors were closing, which I wasn't happy with, but these things happen.
"A lesson learned for both London Underground and commuters with babies to be extra diligent."
Pete Allaway, Circle and Hammersmith line manager, said of last Wednesday's incident: "I'd like to thank the quick-thinking actions of our staff who acted in a calm, professional manner throughout, and I'd also like to thank the customers on the train who alerted the driver and stayed with the baby until the train could be met by station staff."