Sixty-eight immigrants found in Harwich International port lorries
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 Border Force checks at Harwich International Port on Thursday night.
Thirty-five people from Afghanistan, 22 from China, 10 from Vietnam and one Russian were found, at about 22:00 BST.
Four Polish lorry drivers have been arrested on suspicion of facilitating illegal immigration.
They are now being questioned, the Home Office confirmed.
A 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 as a precaution after they reported abdominal and chest pains.
Their conditions are described as non life-threatening.
Bernard Jenkin, MP for Harwich and North Essex, said the people were discovered in trucks "full of Polish washing machines", adding the 68 individuals would probably be told to "go home".
He said 94% of trucks go through unchecked and it was therefore possible more migrants got through this way than was known.
A spokeswoman for Stena Line, the operator of the Stena Hollandica ferry that transported the lorries, said the service left the Hook of Holland at 14:15 BST on Thursday.
It is not yet clear where the lorries had been before sailing to Harwich. The ship arrived at the Essex port at 19:45 BST.
Stena Line confirmed all 68 immigrants were in the care of Border Force at Harwich Port. It is believed those not seeking asylum will be sent home.
Leigh Daynes, executive director of Doctors of the World UK which provides medical aid to undocumented migrants throughout Europe, said: "Over and over we see migrants who have risked life and limb to cross Europe.
"With few safe routes to enter the continent, many more will continue to take dehumanising and perilous journeys like this."
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.
Matthew Broad, from the East of England Ambulance Service, 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."
Analysis: Danny Shaw, Home Affairs Correspondent
The tragic deaths, 15 years ago this month, of 58 Chinese people in a lorry which had been searched at Dover was the first, and clearest, indication of an emerging problem: people smuggling.
Migrants seeking a better life pay criminals to help them reach their destination.
But the routes, typically through northern Africa and southern Europe, or via Turkey and eastern Europe, are hazardous.
In the year to April, almost 41,000 so-called "clandestine" migrants were detected - the vast majority picked up by British staff at joint border controls in northern France and Belgium.
But there's anecdotal evidence that because security is so stringent there, migrants are finding other ways to enter the UK: nearly 1,500 were discovered at ports in Britain - including Harwich.
However, we may never know how many have got in without the authorities finding out.