Police in the UK have launched a murder investigation in southeast England after 39 people were found dead in a truck container at an Essex industrial park. One of the victims was a teenager.

Authorities believe the truck, which originated in Bulgaria, entered the UK through the Welsh port of Holyhead over the weekend. A regular ferry service connects Holyhead with the Irish capital, Dublin.

They have arrested a 25-year-old Northern Irish truck driver “on suspicion of murder” after finding the bodies early on Wednesday morning, Essex Police said.

“We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue ” Mariner added.

“This is a tragic incident where a large number of people have lost their lives. Our enquiries are ongoing to establish what has happened,” he said.

Police have placed a cordon around the area and say they are working with the local council “to mitigate against any impact our investigation scene will have locally.”

The UK Home Secretary, Priti Patel, said she was “shocked and saddened” by what she called the “utterly tragic incident,” according to her Twitter account.