The Minneapolis Star newspaper reported relatives and friends identified the man as Philando Castile, 32. Castile was a cafeteria supervisor at a school in St. Paul school district, according to the paper.
"Oh my God, please don't tell me he's dead, please don't tell me my boyfriend just went like that... You shot four bullets into him, sir," the woman, identified on her Facebook page as Lavish Reynolds, is heard saying.
Castile can be seen in the driver seat, large blood stains spreading through his white shirt. Ms Reynolds was sitting in the front passenger seat. Her young daughter was also traveling in the car.
The incident comes hours after the fatally shooting a black man in Baton Rouge, Louisiana on Tuesday.