An anonymous tip led police to the child at the station on W. 34th Street and 7th Avenue just before 9:30 a.m.
The baby girl was found wrapped in a blanket at the bottom of a staircase leading to the 1/2/3 train platform.
Police say surveillance video shows the woman in question outside Penn Station and they are working to determine what her connection is to the newborn.
The baby was taken to a local hospital by police and was said to be conscious and alert. Her condition was described as stable.
New York City Transit President Demetrius Crichlow called that "the miracle on 34th Street."
"I'm calling it the 'Miracle on 34th Street,' the FDNY and police department responded, they found a baby that was unattended," Crichlow said. "The baby was taken to the hospital and is in stable condition, we don't have any other additional information on top of that, but just grateful for the work of the NYPD for responding and caring for the baby."
New York's Safe Haven Law was created to protect unwanted babies, allowing parents to legally and anonymously abandon a newborn. The baby has to be under 30 days old and left in a suitable location like a hospital or a staffed police or fire station.
The baby can be left in a Safe Haven Baby Box but someone most be notified. To get help or find a location, there is a Safe Haven hotline -- 1-888-510-BABY.
Police say the woman on surveillance is wanted for questioning in connection with endangering the welfare of a child.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
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