Five men have been arrested on suspicion of illegal entry into the UK after a group of men were seen getting out of the back of a lorry.
A witness reported seeing the men leaving through the back of the trailer, near B&Q's distribution centre in Highworth Road, Swindon, on Friday.
They said the lorry appeared to have a hole cut in the roof of the trailer.
Wiltshire Police also arrested the driver and are searching for two other men who they believe left the lorry.
A member of the public called the police shortly after 12:00 GMT on Friday after seeing a number of men leaving the back of the trailer, with one man remaining on the roof.
The driver and one other man were arrested at the scene and officers located four other men nearby shortly afterwards.
Insp Louis McCoy of Wiltshire Police said: "We are keen to hear from anyone who may know where these remaining men might be.
"Whilst we believe they may have illegally entered the UK, we are also concerned for their welfare."