British police found the bodies of 39 people in a truck container at an industrial estate to the east of London on Wednesday.
Police said the truck was believed to have come from Bulgaria and to have entered Britain at Holyhead in Wales on Saturday. The driver, a 25-year-old man from Northern Ireland, has been arrested on suspicion of murder, police said.
“We are in the process of identifying the victims, however I anticipate that this could be a lengthy process,” said Chief Superintendent Andrew Mariner.
“We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue.”
The emergency services said the bodies were discovered in the container at Waterglade Industrial Park in Grays, located by the River Thames about 20 miles from central London.
The 39 victims, 38 adults and one teenager, were all pronounced dead at the scene.
“Such tragic news on loss of life,” Brandon Lewis, a junior interior minister said on Twitter. “Thoughts are with victims, their families & friends. Police are working to ensure those responsible are brought to justice.”