The motorway was brought to a standstill as officers armed with semi-automatic weapons stopped the car near Ketley.
A witness reported that five or six marked police cars were stopped on the motorway as officers trained their guns at a suspect lying on the carriageway.
Traffic heading towards Shrewsbury was not affected by the incident which happened between junctions 6 and 5 at around 4.30pm.
"As I drove past there were armed police all over the road pointing their guns at a man lying on the floor," the witness explained.
"I don't know if they had been chasing him but there must have been five or six marked cars there and it had only just happened.
"All the cars heading to Birmingham were stopped behind the police but my side going towards Shrewsbury was still open."
West Mercia Police has been contacted for comment.