Man dies in Britain as 35 people found in shipping container
Two of the group, believed to be from the Indian sub-continent, were taken to hospital in serious but not life-threatening condition, while others were treated for dehydration and hypothermia.
The container was being unloaded at Tilbury docks in Essex from a ferry that had arrived from Zeebrugge, Belgium.
Essex police said that for the time being they were treating the incident as a homicide investigation.
"As a result of the ferry docking, staff at the port became aware of screaming and banging coming from the container," Superintendent Trevor Roe told reporters.
An East of England Ambulance spokesman added: "It was a very difficult scene for our first crews there."
Port staff were busy searching other containers from the ferry in case there were more people inside.
No further details were immediately available of how long the group had been inside the container or where they had entered it.
Tilbury, on the River Thames, is primarily a bulk cargo and container port and not such a prime target for illegal immigrants as those on the south coast, such as Dover.
Immigration and health authorities were helping the investigation, police said.