A person saw the parked lorry in Palace Road, East Molesey, and said it looked like the driver was making a delivery and opened the back to reveal the unsolicited passengers.
The police were called shortly after 10am on Monday, December 1.
A Surrey Police spokesman said: "Eight people in total, five women and three men, were discovered in the lorry. All eight people have been arrested on suspicion of immigration offences."
The lorry is thought to have come to the UK from Italy, with the eight men and women believed to be from Somalia.
The UK Visas and Immigration are investigating following the arrests.