Khlong Tan station police were alerted to the accident early in the morning and rushed to the scene with King Chulalongkorn Memorial Hospital paramedics and rescue volunteers.
They found meatball vendor Udom Saengkanya, 49, dead on the street with a mutilated skull and broken limbs.
They also noticed a woman standing next to the white BMW parked nearby. Officers said she looked confused.
They learned that after the car hit Udom, the driver called for a van to pick him up and fled the scene.
The woman was still in shock and unable to provide the police with any useful information.
The police have collected footage from surveillance cameras and hope to identify the offender.