A couple was arguing on a CTA Red Line train Thursday when the man suddenly stabbed his girlfriend repeatedly, killing her, police said Thursday.

Jessica Hampton, 25, was stabbed in the neck on a southbound train near the 47th Street station at 12:33 p.m. after an argument, apparently over a child, authorities said.

Hampton, who lived in the 6600 block of South Laflin, was pronounced dead at the scene at 1:15 p.m., the Cook County medical examiner’s office said.

Passengers on the train called 911 to report the stabbing, and an officer was already near the 47th Street Red Line stop as the train pulled up, CPD spokesman Anthony Guglielmi said.

The suspect stepped off the train, saw the officer and surrendered, Guglielmi said.

Police still are conferring with prosecutors on charges. The weapon was recovered at the scene.

The woman was dead when officers arrived, Guglielmi said. He could not say how many times the woman was stabbed.

Investigators are reviewing CTA surveillance camera video of the altercation.

“This is domestic in nature,” First Deputy Supt. John Escalante said at a brief news conference on the slaying Thursday. “We’re sure of that.”

The stabbing happened in the Grand Boulevard neighborhood on the South Side.

CTA workers direct Red Line passengers away from the 47th Street Red Line platform Thursday, after the stop was shut off after a woman was fatally stabbed on the train. | Andy Grimm/For the Sun-Times

CTA workers direct Red Line passengers away from the 47th Street Red Line platform Thursday, after the stop was shut off after a woman was fatally stabbed on the train. | Andy Grimm/For the Sun-Times