The Cobb County Police chief says a Georgia police officer who was heard on a dashcam recording during a traffic stop telling a woman that US police "only kill black people" will be fired.

The dash cam video shows the Cobb County police officer standing by a car pulled over alongside a road last year and instructing the woman in the front passenger seat to use the cellphone in her lap to make a call.

"Ok I just don't want to put my hands down," the woman tells the officer, adding that she has seen "way too many videos of cops", before trailing off.

"But you're not black," the officer replies. "Remember, we only shoot black people. Yeah. We only kill black people, right? All the videos you've seen, have you seen the black people get killed?"

WSB-TV in Atlanta, which aired the video on Wednesday after obtaining it through public records laws, identified the officer as Lieutenant Greg Abbott.

Numerous videos from dash cams, body-worn cameras and cellphones in recent years have shown US police officers killing unarmed black people during encounters, sparking debate about excessive use of force and racial disparities in the criminal justice system.