A man has been arrested after a group of people fled from the back of a lorry stopped on the M6.
Police are working with immigration officials, while the northbound carriageway remains closed.
Burton Albion fans travelling to their Carabao Cup semi-final against Manchester City were among those stuck in the traffic.
Hundreds were yet to arrive at the Etihad as the game kicked off at as planned at 7.45pm.
Staffordshire Police said officers stopped a vehicle on the M6 before “a number of people have exited the back of the vehicle”.
Danny Ellis, who was a few hundred yards from the incident, said he saw 30 to 40 police cars pass him on the northbound side of the motorway and said three or four lorries were stopped and searched.
“We could only see the lorries being chased down and stopped but we couldn’t see people running away,” he told the Press Association.
“We were told for safety to get back in our cars and lock them. We were told a lot of people escaped and ran from the back of these lorries.”
The 30-year-old, who works in the telecoms industry, said he could see men being treated by ambulance medics on the floor.
He was driving to the football with a friend when both carriageways of the motorway were closed between junctions 15 and 16, near Stoke-on-Trent on Wednesday afternoon.
“We’ve been stuck here still for three hours and we’ve been told 10pm,” he added.
Police said in a statement a man was arrested at the scene and is in being held custody, while firefighters and ambulance crews are also on the scene.
“Police and partners are assessing the welfare of the people who exited the vehicle and we will be liaising with our colleagues in Immigration Enforcement,” the force said.
“The southbound carriageway is now open and the northbound carriageway remains closed for the time being.
“We recognise the disruption this is causing to road users and we thank everyone for their co-operation.”