A South Carolina cop saved a lady who repeatedly mouthed "help me" during a traffic stop as her supposed hijacker sat next to her.

Official Kayla Wallace halted a white Jeep on 28 May after it went through a red light, and moved toward the lady behind the wheel.

The driver told the officer the man in the passenger seat had kidnapped her at gunpoint after the shooting.

The suspect, Collins Bates, 29, was arrested.

Ms. Wallace, an officer with the North Myrtle Beach Police Division, knew nothing about the shooting before the traffic stop, Officer Pat Wilkinson told the BBC's US media accomplice CBS News.

There were just 30 minutes left on her shift when Ms. Wallace encountered the vehicle.

After she pulled the vehicle over, police said the driver opened the door and appeared distressed.

"I gave loud orders for her to close the door," Ms. Wallace wrote in a police report. "The passenger also opened his door and stated that the windows don't roll down.

"The driver then told me that she felt like she was going to throw up."

The department posted on Facebook: "While the male passenger wasn't looking at the driver, the female silently mouthed 'Help Me' repeatedly."

Ms. Wallace placed Mr. Bates in the back of her patrol car.

She went back to speak with the driver, who told her that the man had just shot someone before forcing her to drive him away at gunpoint.

During the traffic stop, a "be on the lookout" alert was dispatched over Ms Wallace's radio. It said a white Jeep had been involved in a shooting in the county.

The dispatch also described a suspect matching Mr. Bates' description.

County law enforcement was called to the scene and he was arrested.

He faces charges of attempted murder, kidnapping, and possession of a weapon during a violent crime in connection with a shooting.

Police said a pistol was found under his seat in the car.

"Our department and our community are lucky to have Officer Wallace," the department said.

Kudos to you Ma'am.