British police have said that 39 people found dead in a truck container near London are believed to be Chinese nationals.
Emergency workers made the discovery on Wednesday inside the refrigerated container of a truck parked in an industrial area in Grays soon after it had arrived on a ferry from Belgium.
Essex police said in a statement that eight of the dead were women and 31 were men. China's foreign ministry said its embassy staff in London would go to the scene to verify the situation.
Police also confirmed that officers had searched three properties in Northern Ireland in connection with the investigation. The addresses are believed to be linked to the truck driver who was detained at the scene.
"We arrested a 25-year-old man on suspicion of murder, who remains in custody," police said, adding that they were not identifying him.
Police said a coroner would try to establish the cause of death of the 39 victims, before investigators attempt to identify each individual.
"This will be a substantial operation and, at this stage, we cannot estimate how long these procedures will take," Essex police said.
The container section came by ferry from the Belgian port of Zeebrugge into Purfleet on the River Thames estuary - a crossing that takes between nine and 12 hours.
The vessel docked there at around 12.30am on Wednesday and the truck left the port area about half an hour later.
Emergency services were then called to the Waterglade Industrial Park at around 1.40am.
Prosecutors in Belgium have launched their own inquiry and confirmed Thursday that the container had passed through Zeebrugge, one of the world's biggest and busiest ports, on Tuesday.
"It is not yet clear when the victims were placed in the container and whether this happened in Belgium," the Belgian federal prosecutor's office said.
Essex police revealed the tractor unit of the truck entered Britain on Sunday on a ferry from Dublin to the port of Holyhead. They had earlier said they believed the tractor unit originated in Northern Ireland.
The vehicle had licence plates issued in Bulgaria after it was registered there in 2017 by an Irish citizen, according to the Bulgarian prime minister Boyko Borisov.
He said the unit had not entered Bulgarian territory since.