A dead man was among 35 immigrants found in a container at Tilbury Docks after crew were alerted by "banging and screaming".
Police have launched a "homicide" investigation after the man was discovered with 34 sick children and adults hiding in a container on a P&O ferry.
Police at the scene in Tilbury Docks At least seven of those treated at three different hospitals with "significant health problems" were children.
At a press conference at Tilbury Docks, Essex Superintendent Trevor Roe said the man's death was being treated as a crime.
Seven ambulances were sent to the scene and Basildon Hospital said on its Twitter feed that it was "responding to a major incident".
The East of England Ambulance service confirmed a hazardous area response team had also been sent to the scene.
Eighteen patients were taken to Basildon Hospital, nine to London Whitechapel Hospital and seven to Southend Hospital.
Some were suffering from severe dehydration and hypothermia.
A police officer at the scene said they are still trying to determine the nationalities of those involved but they are believed to be of Indian origin, possibly Punjab.
Basildon Hospital is responding to a "major incident" Essex Police were called after the people were found on the container, which arrived on a ship from Zeebrugge in Belgium and was being unloaded at 7.35am.
Natalie Hardy, from P&O Ferries, said the immigrants were in a container on board the Norstream, a commercial vessel.
She said the ship was scheduled to leave Zeebrugge last night at 10pm and arrive at Tilbury today at 6am.
It was carrying 64 containers, 72 trailers and five lorries and drivers.
The suspected immigrants were found at Tilbury Docks Ms Hardy said: "They (port authorities) found 35 clandestines on a container in the ferry.
"They had been in there overnight, because the ship was an overnight freight ferry.
"This morning when they went to unload containers there was a noise heard, a banging. One unfortunately was dead and others were taken to hospital."
A spokeswoman for Public Health England said it was not involved in the response to, investigation of or anything to do with the incident at Tilbury Docks.
She 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."
Police are dealing with the incident alongside staff from Port of Tilbury, UK Border Force and the East of England Ambulance Service, the spokesman said.
'It's my own freedom here. I can do whatever I want to do'
Some councillors say clubs should try to use funding more wisely
Julie Wharton's Moss Side club needs £50,000 to stay open
The paper published the ad last week
A Palestinian family wait to cross from Gaza into Egypt
Paul Kohler (l) was left with severe injuries after the attack
The man was spotted removing a pair of surgical gloves
The last images of the suspect as he leaves the area in SW19 
Neil Taylor is the only player of Asian descent in the Premier League
Hopes are high for brothers Adil and Samir Nabi
Michael Chopra playing for Blackpool
El-Wahabi will be sentenced on September 12
Ms Msaad, left, said she never meant to smuggle cash to bankroll terrorism
Girls from Newcastle High School celebrate their A-level results
Final grade exams are not published in the DfE's data
Teachers believe extra-curriculum activities should be included in tables 
One of the investigations relates to the victims of Harold Shipman
Tian Tian has a lack of appetite and is very sleepy
Displaced people from the Yazidi sect fleeing the violence in Iraq
A British place prepared to airdrop aid over Iraq
The US has been carrying out targeted airstrikes in Iraq
Muhammad Hamidur Rahamn has reportedly been killed in Syria. Pic: Facebook
A crane attempts to remove a fallen tree in Hull on Sunday
Many areas were flooded on Sunday, including parts of Grimsby
HMRC says the proposals will only affect a small minority of wealthy people
Parts of the race had to be cut due to bad weather
Baroness Warsi quit the Foreign Office over Gaza last Tuesday
David Cameron is currently away on a family holiday in Portugal
The Mail On Sunday front page
Bill Etheridge urged candidates to "pick up moments" from Hitler speeches
DNA technology helped police convict serial killer Steve Wright
Vincent Tabak was matched to DNA found at Joanna Yeates' murder scene
Prince Harry served as an Apache helicopter pilot
The Royal flew injured soldiers to the hospital at the Camp Bastion base
The festival was being held at Matterly Estate in Winchester, Hamphire
The Met Office has issued a yellow rain warning for much of the UK
Waves crash against the rocky coastline of Milford on Sea
A woman braves the strong winds and rain in Brighton
Tourists in central London battle the elements
The A14 in Cambridgeshire was flooded on Friday