Twenty-seven suspected migrants have been detained after a lorry was stopped on the M6 and some of the group fled, Staffordshire Police said.
The motorway near Stoke-on-Trent, Staffordshire, was closed in both directions on Wednesday night after police declared a “major incident”.
Hundreds of motorists were trapped between junction 15 and 16 after stopped a vehicle which contained a number of people.
The driver, who was arrested at the scene, is being quizzed by immigration enforcement officers.
A statement from Staffordshire Police later said: “An investigation is continuing tonight after 27 people were detained following a vehicle stop on the M6 earlier this evening resulting in total closure of the motorway.
“Officers from Staffordshire Police stopped a lorry on the M6 northbound carriageway between Junctions 15 and 16 at around 5.45pm following concerns for people travelling in the back of a vehicle.
“During the incident, a number of people fled from the lorry but all were detained. Thankfully, there were no serious injuries reported.
“The driver of the vehicle, a 42-year-old man was arrested on suspicion of facilitating the illegal entry of persons unknown to the UK.
“He remains in police custody at Watling Street police station and enquiries are ongoing.”
Burton fans travelling to their Carabao Cup semi-final against Manchester City were among those stuck for hours in the traffic.
A number of eyewitnesses have told Stoke on Trent Live that police have been pulling over and checking lorries.
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.”