Eleven people, including three children, have been discovered in the back of a lorry, police said.
Officers were called to the A303 in West Knoyle, near Warminster, Wiltshire, shortly after 2.15pm on Saturday.
A member of the public reported that they had heard banging from inside the lorry.
Wiltshire Police, assisted by Dorset and Wiltshire Fire and Rescue Service, found 11 people at the back of the vehicle.
A force spokesman said: "These included three children under the age of 15 and eight other people who were all checked over by paramedics at the scene.
"We are currently working with colleagues from the Home Office Immigration Department as our inquiries progress."
Anyone with information is asked to contact Wiltshire Police on 101, quoting log number 160 of December 2.
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