A boy is in hospital with serious injuries after being hit by multiple cars on the M5, closing the motorway in both directions.
The teenager was on foot at the time of the incident, which happened at about 11.15am on Wednesday, West Midlands Ambulance Service (WMAS) said.
Police are now trying to piece together how the youngster came to be on the busy motorway.
In a statement, West Midlands Police said: "The M5 is currently closed in both directions between junctions two and three after a pedestrian was hit by several cars at around 11.15am today.
"The pedestrian, believed to be in his teens, has been taken to hospital with serious injuries.
"Inquiries around how the boy ended up on the motorway are at an early stage."
The incident happened a short distance before the Oldbury interchange and an air ambulance was deployed to the scene as part of the medical response.
A WMAS spokesman said: "The boy was on foot at the time of the incident.
"He has suffered serious injuries.
"He was assessed and treated at the scene before being taken on blue lights to Birmingham Children's Hospital.
"The doctor from the air ambulance travelled with the boy to hospital."
Nobody else needed treatment at the scene.