Lincolnshire Police detained a group of people including women and children on suspicion of unlawfully entering the UK through the county.
The group of seven were caught after they were seen exiting a lorry in Low Fulney in the south of Lincolnshire near Spalding.
An ambulance also attended the scene to treat to a woman in the group suffering from vomiting.
The tip was passed on to police by staff at a premises in Kellett Gate just after 6.30am on February 7.
At present, it is not known where the group originated from, ages, or how many are children.
The group will remain in police custody until being passed on to UK Border Agency staff.