The incident happened on an April morning at the Masmo metro station south-west of Stockholm.
A two-seat pushchair, with a child sitting in the front part, got stuck when the sliding doors closed. The mother was left on the platform when the train departed with the chair still trapped between the doors.
“I heard the mother scream an animalistic scream and saw the train leaving with half of the pushchair hanging out. It was the most awful thing I've ever seen,” witness Erica Eriksson told public broadcaster SVT.
“When the train reached the gate at the end of the platform, the rear end of the stroller hit the gate and was smashed apart, while the child inside the carriage flew further into the train,” explained Fredrik Bouvin, security manager at MTR which operates the metro, to SVT.
The child appears to have been unharmed in the incident. Passengers on board the train took care of the toddler and turned back at the next station to hand them back to their mother within minutes.
MTR has however not been able to reach the mother, who left with her child after the incident and has not been identified, but estimates that the child was one to two years old. Bouvin described the incident as the most serious since the company took over operation of the Stockholm metro ten years ago.
An investigation is currently under way. According to MTR there was no technical fault with the train, one of Stockholm's older models from the 1980s, and initial findings suggest that it was human error.
The driver was taken out of service immediately after the incident.