The 39 people found dead Wednesday in the back of a cargo truck in Essex, United Kingdom, were all Chinese citizens, British police have confirmed.
The Chinese embassy in the UK said: "We read with heavy hearts the reports about the deaths of 39 people in Essex, England. We are in close contact with British police to seek clarification and confirmation of the relevant reports."
Officers are continuing to question the truck's 25-year-old driver from Northern Ireland who was arrested on suspicion of murder.
The bodies were discovered by ambulance staff at Waterglade Industrial Park in Grays, a town 40 kilometers east of London, and authorities were alerted before 1:40 am.
Essex police believe the truck's cab entered the UK via Holyhead, Wales, on Sunday.
The cab and trailer containing the victims apparently took separate journeys before arriving at the industrial park. British authorities said they believe the container went from the port of Zeebrugge, Belgium, to Purfleet, England, where it arrived early Wednesday.
Essex police said in a statement, "We have since confirmed that eight of the deceased are women and 31 are men and all are believed to be Chinese nationals. We arrested a man on suspicion of murder, who remains in custody."
Essex police said the event has "led to the largest murder investigation in our force's history".
The force said one victim previously thought to be a teenager was a young adult woman.
It is the UK's worst such tragedy in almost 20 years since the bodies of 58 Chinese were found in a container in Dover, Kent, in 2000.
Officers also searched three addresses in County Armagh, Northern Ireland, in connection with the investigations.
Media reports suggested the refrigeration unit may have been on and the migrants could have frozen to death in temperatures as low as -25 C.
The truck has since been moved from the industrial park as investigations continue and a post-mortem examination will take place to establish causes of death.
"This will be a substantial operation and, at this stage, we cannot estimate how long these procedures will take," Essex police said. "The process will be complex and lengthy, as well as incredibly challenging for all those involved, but we will not stop until we get answers for the loved ones of those who have sadly died."
The National Crime Agency said it was assisting in the investigation and working to "urgently identify and take action against any organized crime groups who have played a role in causing these deaths".
The Belgian federal prosecutor said in a statement on Thursday that it had opened an inquiry into the deaths of the 39 people.
"The investigation will focus on the organizers of and all other parties involved in this transport," the prosecutor said.
Maurice Wren, chief executive of the London-based Refugee Council, said: "This is truly tragic news, but depressingly predictable and avoidable news. If you deny people safe and regular travel routes to find safety, you are leaving them with no choice but to risk their lives on utterly perilous journeys and in the hands of criminal gangs. These gangs are a symptom of a much deeper problem — namely governments' failure to provide safety to those who desperately need it."