Tilbury container stowaways included 13 children
Thirteen children aged between one and 12 were among 35 Afghan Sikh immigrants found in a shipping container at Tilbury Docks, Essex Police have said.
The group arrived on Saturday on a ship from Belgium and were said by police to be victims of "people trafficking".
One man was found dead and the others were taken to hospital to be treated for severe dehydration and hypothermia.
The 30 people released to police include nine men and eight women aged between 18 and 72.
They have been brought to a makeshift reception centre set up inside the terminal buildings at Tilbury Docks.
Police said they are "being spoken to about their ordeal" before they are passed on to the UK Border Force.
The other four people discovered in the container remain at Southend Hospital.
Essex Police said the stowaways are to be interviewed to find out how they came to be inside the container.
Police launched a homicide investigation following the death of the man, who is thought to be in his 40s.
A post-mortem examination was carried out on Sunday but police say further tests need to be undertaken to establish the cause of death.
The container is being forensically examined, they added.
Officers are working with Interpol and other international authorities to try to establish what happened.
Supt Trevor Roe of Essex Police said: "The welfare and health of the people is our priority at this stage.
"Now they are well enough, our officers and colleagues from the Border Force will be speaking to them via interpreters so we can piece together what happened and how they came to be in the container.
"We now understand that they are from Afghanistan and are of the Sikh faith.
"We have had a good deal of help from partners within the local Sikh community in the Tilbury area to ensure that these poor people, who would have been through a horrific ordeal, are supported in terms of their religious and clothing needs."
The Red Cross provided food and welfare for the group overnight.
Immigration lawyer Harjap Singh Bhangal told the BBC that the Sikh community in Afghanistan had long complained of harassment.
He said the number of Sikh families had been "dwindling" and they faced verbal and physical abuse.
He said: "As a result Sikhs are leaving Afghanistan, and they feel persecuted, and they're leaving for other countries in Europe such as Germany, France and the UK."
Sikhs in Afghanistan
By Inayatulhaq Yasini, BBC Pashto
The history of Sikhs in Afghanistan goes back about two centuries. In the 1970s they are thought to have numbered about 200,000, with most living side-by-side with other communities in cities like Kabul, Jalalabad and Kandahar and involved in the fabrics and clothing business.
But the population is now thought to number less than 5,000. After the Soviet invasion in 1980, a great number migrated to India. A second phase of migration took place after the fall of communist government in 1992. And during the civil war that followed, Sikh business and homes were occupied. They were forced to leave the country with other minorities, including Hindus.
During the Taliban era, Sikhs gained some independence. However, they were forced to wear yellow patches in order to be "recognised or differentiated" from other Afghans.
After the US invasion in 2001, Sikhs were given more freedom by Hamid Karzai's new government. But even now they are in dispute with the government over their custom of holding outdoor cremations.
Until recently, Sikhs did not have any representation in the Afghan Parliament. However, last year President Karzai allocated a seat for them, which will be shared with a Hindu representative.
'Screaming and banging'
The discovery was made after the container arrived from the Belgian village of Zeebrugge at about 06:00 BST on Saturday when "screaming and banging" were heard coming from inside.
All the remaining containers on the ship have been searched and no-one else has been found.
Essex Police said there were initial concerns more people could be inside a container that arrived at Purfleet but that this turned out not to be the case.
Belgian police said they believed the lorry which delivered the container in Zeebrugge had been identified through CCTV footage.
Chief Inspector Peter De Waele said it was likely the people were already inside the container when it was dropped at Zeebrugge as it appeared "impossible" the group could have entered it during the hour it was at the port.
It is not known where the container, one of 64 aboard the P&O commercial vessel Norstream, originated, nor where the people inside it were heading.
'Exploited by gangs'
Former head of the UK Border Force Tony Smith said those inside the container were victims of international organised criminals.
He told the BBC: "They're being exploited because the prize is a passage to the West - that's what they want, they want to migrate to the UK or to Europe but they're being exploited by criminal gangs who are probably taking their entire life savings away on the promise of a passage to the West.
"We really need to get a message out to migrants that if they want to come to this country there are legal routes that they need to explore and they need to apply for visas and permits."
Anthony Steen, chairman of the Human Trafficking Foundation, said: "It shows how desperate people are to improve their economic situation - how desperate they are to leave their own homes, and own countries, and hope to arrive in somewhere that's more accommodating, more kind, and offering them a better quality of life. Usually, they're sadly wrong."
Police have set up a "casualty bureau" hotline for anyone concerned about relatives. The numbers are 0800 056 0944 or 0207 158 0010 if dialling from outside the UK.