Police said a member of the public reported seeing men jump out of the doors of a container attached to a lorry.
The incident occurred on the Lady Lane Industrial Estate while the vehicle was parked on the road outside a unit.
AnneMarie Breach, a spokeswoman for Suffolk Constabulary, said the men were seen looking around when the got out of the container.
Another member of the public also called police to say they had seen four males who they thought might be illegal immigrants.
Four of the men in were found in Red Hill Road, near the Hadleigh bypass. Another two males were discovered elsewhere in the town.
A short time later two young adult women were also detained after went into Hadleigh police station.
The first report to police was made at around 8.55am on Monday and the suspects were in custody by 11.30am.
They were taken to a police investigation centre and handed over to the UK Border Agency.
A spokesman for UKBA said: “Six males – five from Eritrea and one from Sudan – and two women from Eritrea were arrested on suspicion of immigration offences.
“One of the Eritrean males was subsequently independently age assessed as a minor and passed into the care of social services.
“The others have been transferred to immigration detention where they remain.”
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