Police, paramedics and the fire service rushed to the Asda Queslett store, off Queslett Road in Great Barr, at around 6pm today.
People on social media have reported seeing "seven ambulances, two fire engines and numerous police cars" pour into the car park.
A spokesman for West Midlands Police said: "Police and paramedics were called to the car park at Asda Queslett at 6pm today following concerns for a man who appeared unconscious inside a vehicle.
"It quickly became clear there was nothing that could be done to save the man. His death is not believed to be suspicious."