Pictures: The discovery of 39 bodies in a lorry container in Essex
A 25-year-old-man from Northern Ireland has been arrested on suspicion of murder after 39 people were pronounced dead at the scene in Grays, Essex.
Early indications suggest 38 are adults and one aged in their teens, police said.
"We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue."
Home Secretary Priti Patel tweeted: "Shocked & saddened by this utterly tragic incident in Grays. Essex Police has arrested an individual and we must give them the space to conduct their investigations."
A restaurant worker in the industrial estate, who did not want to be named, said the area was cordoned off by police on Wednesday morning. "There's a lot of police and forensics"
Richard Burnett, chief executive of the Road Haulage Society, said "this tragedy it highlights the danger of migrant gangs people-smuggling on lorries".