A lorry driver is being questioned after 27 suspected migrants were found in the back of his vehicle on the M6.
A part of the motorway was closed in both directions after police stopped and searched the lorry at around 5.15pm on Wednesday.
All of those on board were medically assessed and transferred to immigration officials for interview, it is understood.
The driver, who was arrested by Staffordshire Police at the scene is being quizzed by immigration enforcement officers.
Burton fans travelling to their Carabao Cup semi-final against Manchester City were among those stuck for hours in the traffic.
Hundreds were yet to arrive at the Etihad as the game kicked off as planned at 7.45pm.
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 said at around 8pm.
Police said in a statement officers stopped a vehicle on the M6 before "a number of people have exited the back of the vehicle".
"A man was arrested at the scene and is being held in custody, while firefighters and ambulance crews are also on the scene," the force said.
"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."