A driver alerted Northamptonshire Police after he discovered a large group of illegal immigrants had stowed away in his lorry this afternoon.
The HGV was near the Royal Mail depot in Danes Way - part of the DIRFT rail site near Crick - at about 1pm when police were alerted.
About five police cars were sent to the scene and a total of 21 immigrants were discovered in the vehicle.
A police spokeswoman said the stowaways - who, it is believed, were all young men - were being medically assessed and would be taken to the Criminal Justice Centre at Brackmills.
It is understood that the lorry had Romanian number plates and had recently travelled from Calais.
Joe Reid, who witnessed the incident, said: “They didn’t appear to be distressed or causing any problems, they were just being led away by the police.”