A female MTA conductor was sprayed in the face with an “unknown liquid” in an unprovoked attack in Manhattan Friday morning, cops said. 

The assailant approached the 39-year-old woman at the window of a train that had pulled into the 81st Street-Museum of Natural History station around 8:30 a.m., authorities said. 

Without any prior interaction, he discharged the substance at the worker and took off, cops said. 

Photos show EMS workers examining the woman’s eye and treating her at the scene. 

The suspect was still on the loose later in the morning.