An unidentified woman was fatally wounded Monday night during an argument on a CTA Red Line platform, Chicago police said.

About 9:45 p.m., the victim was involved in an argument on a Red Line platform in the first block of West 69th Street with another woman when the person she was arguing with pulled out a handgun and opened fire before fleeing the scene, police said.

The victim suffered a gunshot wound to the neck and was taken in critical condition to UChicago Medicine where she later was pronounced dead.

No one was in custody for the fatal shooting and detectives were investigating.