A subway rider abandoned a baby girl at the Columbus Circle subway station Monday — by pushing her stroller from the train and onto the platform seconds before the doors closed.

A witness told cops the woman was walking with the stroller in the first car of the uptown No. 1 train at about 11:50 a.m., then shoved it out when they arrived at the busy station.

A good Samaritan waiting for the train went over to the red stroller and found a 7-month-old girl wearing a white and red blouse, black leggings and diapers.

Catherine Boursier, 52, waited with the baby until she found two cops on anti-terror patrol about 20 minutes later, sources said.

The officers took the child to the Transit District police station inside the subway station.

The baby was brought to Roosevelt Hospital for an evaluation and she will be turned over to the city Administration for Children’s Services.

The infant — who had a rash on her face and bandages on her hand — had not been identified, and her family has not been located.

The woman who abandoned her was captured on surveillance video entering the Times Square station at around 11:30 a.m. She wore a white tank top while pushing the polka-dotted stroller through the gate.

“What could possess somebody to do such a cruel thing?” asked Tanya Ortiz, a 37-year-old mother from Astoria, Queens. “Thank God that [Samaritan] was there to watch the little girl. There are better ways to go about this. This was just so cruel.”

Other riders at the Columbus Circle station were stunned someone had left a child there.

“I think it’s real sad. Whoever left that baby on the platform has some serious problems,” said Ashley Marrion, 29, of Hamilton Heights.

Liz Burchfield, 34, of Manhattan, said the woman must have acted in desperation.

“I just think: Oh, God, there’s no way she was in her right mind,” she said. “What mother could do that to her child or to any child? I’ve heard horror stories about bad things happening on trains, but this is a first. It’s shocking. I never would have expected this.”

Additional reporting by Harrison Marder