The 39 people found dead in a shipping container attached to the back of a truck in Southeast England on Wednesday were all Chinese citizens.
Essex police confirmed the news in a statement Thursday, saying 31 of the deceased were men and eight were women. They added that it will take some time to identify the victims and figure out the cause of death.
China's Foreign Ministry said the country's embassy employees in the U.K. were sent to the scene of the crime to help with the investigation. Belgium has also opened an investigation into the deaths, as police now believe the container came into England from Belgium, while they believe the truck came from Northern Ireland.
The driver of the truck, a 25 year-old man from Northern Ireland, was arrested Wednesday on suspicion of murder. Police said they "have secured a warrant for further detention ... and [he] will now remain in custody for up to an additional 24 hours."
Prime Minister Boris Johnson said he's appalled by the incident, and said the Home Office is working with police to determine what happened. U.N. Secretary-General Antonio Guterres said he was "horrified and deeply saddened" by the news, and extended his "deepest condolences to all who have lost family and loved ones."
Essex Police said the case was the largest murder investigation in its history, adding it is working "diligently to piece together the circumstances of this horrific event."
Additional reporting from Newsy affiliate CNN.