Sixty-eight suspected illegal immigrants, including two pregnant women and 15 children, have been found locked inside four lorries after a routine port search.
Four Polish lorry drivers were arrested on suspicion of facilitating illegal immigration after the discovery at Harwich International Port in Essex at about 10pm yesterday.
On board the lorries were 35 Afghan nationals, 22 Chinese nationals, 10 people from Vietnam and one Russian.
Seven of them - including the two pregnant women - were taken to Colchester General Hospital to be checked, before being released into the care of Border Force officials.
A Home Office spokesman said: "We can confirm Border Force officers discovered 53 adults and 15 children during a proactive search of four lorries which had arrived at Harwich port from Holland on Thursday evening.
"Four Polish nationals, who were driving the vehicles, have been arrested on suspicion of facilitating illegal immigration.
"They have been taken to separate police stations and will now be questioned by the Home Office's criminal investigations team while inquiries continue."
All 68 individuals are now in the custody of the Border Force.
A spokesman for the Essex port said the people were discovered on vehicles that had arrived on a ferry from Holland.
A spokeswoman for Stena Line said: "We can confirm that four different lorries carrying 68 clandestines were stopped by Border Force at Harwich International Port last night as they disembarked from the Stena Hollandica."
She added that the ship left the Hook of Holland at 2.15pm and arrived in Harwich at 7.45pm yesterday - a five- and-a-half-hour journey
The British Red Cross said staff and volunteers were responding to the immediate needs of the 68 immigrants found on the lorries.
It confirmed that all of the non-European migrants were found locked in four separate vehicles, and that the charity was providing practical and emotional support, including blankets, food and hygiene packs to those affected.
A spokesman for the UN High Commissioner for Refugees (UNHCR) said the priority was to find out who the people are, their needs, and whether they are entitled to any protection.
He continued: "The situation we have here is consistent to what we have seen elsewhere. It shows the desperation and vulnerability of those who might have been seeking protection across the UK.
"It also shows the dangerous and unscrupulous methods used by traffickers and smugglers."
Following a search at Harwich last February, two illegal immigrants plunged to their deaths after jumping from a ship in an attempt to swim to shore.
Artur Doda, 24, and Leonard Isufaj, 27, both from Tirana, Albania, were seen leaping from one of the world's largest ferries, the Stena Britannica, about 1,600ft off Harwich at about 9.50am on February 26.
They had been found in the back of a lorry along with 13 others of mixed nationalities after it was randomly selected for X-ray as it entered the port six hours earlier.
An inquest at Chelmsford heard that Mr Doda was sliced to death by the "machete-like" motion of the ship's propeller and Mr Isufaj drowned after they were both sucked underwater almost immediately after jumping over the side, 10 minutes into the journey back to the Hook of Holland.
Mr Isufaj's body was found on March 20 on Felixstowe beach while Mr Doda was found floating in the water off Essex on April 29.
Coroner Eleanor McGann recorded that both men died accidental deaths, adding that it was difficult to make recommendations to the Government based on this case.
"This is all part of a bigger picture on immigration and how it's handled, and nothing I could say could help prevent such sad deaths in future," she said.