Part of the M6 has been closed after a number of people were found in the back of a lorry stopped by police.
Motorists have reported being stuck in standstill traffic since about 16:00 GMT after the vehicle was stopped near Keele services.
Staffordshire Police declared a major incident and warned drivers to find alternative routes.
A man has been arrested the force said it “will be liaising with colleagues in immigration enforcement”.
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.
The northbound carriageway, between junctions 15 and 16, remains closed.
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 face missing the Carabao Cup semi-final against Manchester City – one of the biggest games in the club’s history.
Highways England advised people to avoid the area and follow diversions where possible.
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