Police are trying to identify the occupants of the BMW and want anyone who saw the incident or has CCTV to get in touch by calling 101.
Witnesses told officers the occupants of the car were a man and a woman, both of whom were white.
They said the man had short, dark coloured hair and was wearing a grey puffer jacket, light-coloured trousers and white trainers.
The woman was said to have blonde hair and was wearing a black puffer coat, blue jeans and light-coloured shoes.
A spokesperson from the South Western Ambulance Service NHS Foundation Trust, said: “We received a 999 call at 13:51 regarding an incident on Kings Weston Road, Bristol.
“We dispatched a Hazardous Area Response Team, two land ambulances and additional resources to the scene.”
