The child – who appeared to be a newborn – was discovered around 9:30 a.m. on the stairs leading to the southbound 1, 2 and 3 trains at 34th Street-Penn Station, authorities and sources said.

The person who made the startling discovery called 911, drawing first responders to the scene, police said.

The baby, who was conscious and alert, was taken by EMS workers to Bellevue Hospital in stable condition, cops said.

The NYPD is sifting through surveillance footage to find out who left the infant behind, cops said.

No arrests had been made by later in the morning.