Sixty-eight suspected illegal immigrants, including two pregnant women and 15 children, have been found inside four lorries at a port in Essex.
They were discovered during routine checks at Harwich International Port at about 22:00 BST on Thursday.
Among those found were 35 people from Afghanistan, 22 from China, 10 from Vietnam and one Russian.
Four Polish lorry drivers have been arrested on suspicion of facilitating illegal immigration.
They are now being questioned, the Home Office confirmed.
A Home Office spokesman said the stowaways were found inside four separate lorries rather than in one container as initially reported.
The pregnant women were among seven people taken to Colchester Hospital suffering from non life-threatening abdominal and chest pains.
The remaining 61 were assessed and released to immigration officials.
They are currently being held at Harwich port and those not seeking asylum will be sent home, a Stena Line spokesman said.
The ferry set off from the Hook of Holland on Thursday afternoon. It is not yet clear where the lorries had been before sailing to Harwich.
A port spokesman said the stowaways were believed to have been found as part of routine checks being carried out by the Border Force.
Matthew Broad, from East of England Ambulance Service, said the “immigrants were a number of mixed nationals from a number of countries, European and further afield”.
Essex Police said Border Force staff were taking the lead on the incident as it “relates to immigration offences”.
Last August, one man died when 35 Afghan Sikh migrants were found in a container at Tilbury Docks.
They were discovered after dock workers heard banging and screaming coming from one of the containers.
Mr Broad said there appeared to be a “similar pattern” to Thursday’s incident.
“We have experience of dealing with this in Essex, and one of the things we were concerned about was the length of time they’d been in there.”