A police department in the US state of Georgia has started an investigation into one of its officers after he was recorded on a dashboard camera trying to convince a white woman that she had nothing to worry about during a traffic stop because she was not black.

The video, obtained by WSB Channel 2 Action News in Atlanta, shows Lieutenant Greg Abbott of the Cobb County Police Department standing at the side of a car during a traffic stop last year. He tells the woman, a passenger, that she could use her mobile phone.

"It's in your lap right there," he says. She replies that she does not want to move her hands, saying she has seen "way too many videos" about how police behave at traffic stops.

"But you're not black," Abbott replies. "Remember, we only kill black people. Yeah. We only kill black people, right?"