Law enforcement authorities have launched an investigation after they made a grim discovery of 39 bodies in an Essex lorry container.
The truck was discovered in southeastern England.
A 25-year-old man said to be from Northern Ireland is in police custody as investigations continue.
Deputy Chief Constable Pippa Mills said that the priority of the police will be to first identify the 39 victims.
She, however, warned that the process of identifying all the 39 victims will be a lengthy process.
Mills appealed to anyone with information about the lorry to come forward and give it to the police.
Britain's Prime Minister Boris Johnson said that he is aware of the matter and is receiving regular updates from the Home Office.
"I am receiving regular updates and the Home Office will work closely with Essex Police as we establish exactly what has happened. My thoughts are with all those who lost their lives and their loved ones, " Johnson said.
Priti Patel, who is the Home Secretary, expressed her shock at the grim discovery.
Speculation is rife that the 39 people may have been victims of human trafficking, which is illegal under British law.