Police have launched a homicide investigation after the death of a man found trapped with 34 other people in a shipping container at Tilbury Docks in Essex on Saturday morning.

The group were discovered after dock workers heard "screaming and banging" as the container was being unloaded, after arriving from Zeebrugge in Belgium at 6:37am. All of the survivors are being treated in hospital for dehydration and hypothermia.

Police said the suspected immigrants were believed to be from the Indian subcontinent, but said it was too early to confirm their nationalities and ages. They are thought to have been in the container for at least 12 hours overnight, on a commercial P&O ferry, although police declined to say where the container originated from.

The discovery was made early on Saturday morning as the ship was being unloaded by Port of Tilbury authorities.

Superindendent Trevor Roe of Essex police 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. This is a humanitarian issue - the welfare of these patients is a priority."

Emergency services were on the "very difficult scene" within 11 minutes and immediately declared a major incident, setting up a casualty bureau to treat the 34 survivors.

Roe said: "There are 50 containers on that ferry which we are continuing to open and explore to make sure that there are no further incumbents within those containers, which is a concern."

"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."

Detectives investigating the incident are liaising with Belgian police, he added.

Roe also said officers were faced with some language difficulties due to the origin of the 34 survivors. "Some of the difficulties around some of the questions are because we can't speak to them and engage," he said.

Assistant chief officer Daniel Gore from Essex ambulance service said he could not yet confirm how the man had died. He said that none of the people being treated in hospital were thought to have life-threatening conditions, although two had serious conditions.

East of England ambulance service said earlier: "We sent seven ambulances, two rapid response cars, a patient transport services vehicle, two duty operational managers, two BASICS doctors and our hazardous area response team (Hart), a number of which are still on scene.

"After initial treatment by ambulance crews, all patients have now been conveyed to surrounding hospitals for further care; seven have been taken to Southend Hospital, nine to London Whitechapel hospital and 18 to Basildon hospital.

It is understood that those taken to Basildon hospital are not suffering from life-threatening conditions.

A spokesman for Darent Valley hospital in Dartford, Kent, said on Saturday morning that it was "currently on standby to receive cases".

Earlier on Saturday a spokesman for Essex police said: "One man has sadly died and the others have significant health problems. Essex police is working in partnership with the Port of Tilbury, UK Border Force and the East of England ambulance service. A casualty bureau is in the process of being set up."