A 21-year-old New York City woman is in critical condition Friday after being hit in the face with an "unknown chemical substance" on a subway platform in Brooklyn, police say. 

The incident happened around 1 a.m. this morning at the Winthrop Street station "when an unidentified female individual began a verbal dispute with the victim," according to the NYPD. 

"The female individual began following the victim up the stairs and then splashed an unknown chemical substance on the victim's face," police said. "The female individual then fled on foot topside to parts unknown." 

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The female suspect wanted by the NYPD for a subway attack in Brooklyn this morning. (NYPD)

The victim – identified by Fox5 NY as a hospital worker who was on her way to her shift – was taken to a local hospital in "critical but stable condition with burns to the left side of the face," the NYPD says.

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Investigators described the suspect as a female with a dark complexion, medium build and black hair, around 20 to 30 years old. 

The NYPD says the suspect fled the Brooklyn subway station on foot. (New York Police Department)

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She was last seen wearing "a black jacket with a brown fur on the hood, black pants with white drawings on the legs and black boots," the NYPD said. 

The incident happened around 1 a.m. on the "southbound platform at the Nostrand Avenue and Winthrop Street subway station," the NYPD says. (iStock )

The suspect is wanted for assault.