British police have launched a “homicide investigation” after 35 suspected immigrants were found in a shipping container at the Port of Tilbury in Essex.

Superintendent Trevor Rowe said the stowaways, both adults and children, were found in a container that arrived on a P&O ferry from Zeebrugge in Belgium at about 6.30am.

One man died and the others were taken to three hospitals.

Mr Rowe said: “All we know at the moment is that we believe them to come from the Indian subcontinent, but it is still early days.

“It is a homicide investigation from the police point of view at this time.”

The group was discovered after port staff heard “screaming and banging” coming from a container, he added.

He said there were about 50 containers on the ferry and searches were continuing to establish whether any others contained people.

He said: “This is a humanitarian issue and the welfare of these patients is a priority.”

Mr Rowe said a “major incident” was declared at the port at 6.37am.

He said: “Staff here at the port became aware of screaming and banging coming from a container coming from that particular ferry. As a result of that noise, staff were alerted and immediately breached the container to find 35 persons within that unit.”

The group consisted of adults and children of both genders.

The Norstream was described as a “roll-on, roll-off” container ferry. Mr Rowe said: “It is a regular route here twice a day from Zeebrugge.”

Mr Rowe added: “There are 50 containers on that ferry which we are continuing to obviously open and explore to make sure that there are no further incumbents within those containers, which is a concern.”

So far almost 30 of the 50 containers on the ferry have been searched.

“That is the priority issue here at the moment – to make sure that there are no other containers on that particular ship that may or may not contain any persons,” Mr Rowe said.

The unit in question was around the size routinely carried by a large heavy goods vehicle. Mr Rowe said that once the door on the container was opened those inside were extracted “very quickly”.

Asked where the container came from and its movements prior to arrival at Tilbury, Mr Rowe said: “There are 50 containers, that particular container will be the subject of a criminal investigation so we wouldn’t disclose those details at this time.”

All of those found in the container were conscious when it was opened apart from the man who subsequently died

British authorities are understood to be liaising with counterparts in Belgium as part of the investigation into the container’s origins. Mr Rowe said: “It is a homicide investigation... we will be looking to see where the origin and the gangs or whoever may (be) involved in this conspiracy to bring these people in this way over to this country.

“Clearly we need to try and bring them to justice.”

When asked to clarify the nature of the homicide investigation, police said charges could include murder and manslaughter, although there was no suggestion anyone on the container was a suspect.

The superintendent added: “Nothing has been ruled out. We need to speak to the people in the container, where they have come from, what their motivation is and who’s involved.”

He said there was no indication of those on board suffering with a specific virus, but said tests were being carried out at hospital.

Public Health England has said it was not involved in the response to, investigation of or anything to do with the incident.

A spokeswoman said: “If it was ebola, health care professionals are so alert at the moment to signs and symptoms that should there have been anyone who was showing symptoms we would have been notified immediately.

“I think we can be confident that we are not dealing with that.”

Officials are set to interview the stowaways at a reception centre after they are released from hospital. Police said there are “language issues” and interpreters will be brought in.

Daniel Gore, from the East England ambulance service, said paramedics arrived on the scene within 11 minutes and immediately declared it a major incident.

He said: “In terms of the number of patients that we dealt with it is 35 patients in total. Unfortunately one of those patients was declared deceased at the scene, a male.”

No information has been released about the ages of any of the stowaways or the relationship between them.

Two patients were taken to Basildon Hospital in a serious but not life-threatening condition, Mr Gore added, along with 16 other patients suffering from dehydration and hypothermia.