A lorry driver is being questioned after 27 suspected migrants were found in the back of a vehicle stopped by police on the M6.
Part of the motorway was closed from about 16:00 GMT – causing lengthy tailbacks – as police searched vehicles near Keele services.
Staffordshire Police said a man had been arrested at the scene.
It is understood those on board were medically assessed and transferred to immigration officials for interview.
The motorway was initially closed in both directions between junctions 15 and 16 amid reports of large-scale police activity. It fully reopened at about 10pm.
Driver Danny Ellis 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 were told for safety to get back in our cars and lock them,” he said.
“We were told a lot of people escaped and ran from the back of these lorries.”
The 30-year-old telecoms worker said he could see men on the ground being treated by paramedics.
Another eyewitness told BBC Radio Stoke he saw police stopping lorries on the motorway.
“They pulled a white trailer up on the side and they were shouting ‘are they in here?'”, he said.
“The driver opened the vehicle and I just watched 15 of them come out.”
“I did see a few run up the motorway and the police gave chase. Both of those people were brought back.”
Both carriageways have since re-opened, Highways England said.
Staffordshire Fire and Rescue Service and West Midlands Ambulance Service are also at the scene, police added.
Motorists have faced huge tailbacks on the road, including hundreds of Burton Albion supporters.
They were travelling to the north-west to witness their team’s Carabao Cup semi-final against Manchester City. Burton were thrashed 9-0 in the game, one of the biggest in the club’s history.
Highways England advised people to avoid the area and follow diversions where possible.
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