British police said 39 dead bodies were found Wednesday in the container of a truck thought to have come from Bulgaria.
"This is a tragic incident where a large number of people have lost their lives," Essex Police said in a statement, saying the fatalities were pronounced dead at the scene in an industrial park in Grays, east of London.
A 25-year-old-man from Northern Ireland has been arrested on suspicion of murder.
Chief Superintendent Andrew Mariner said Wednesday that authorities are in the process of trying to identify the 38 adults and one teenager. It is expected to be a lengthy process.
Mariner says the truck entered the country on Saturday, Oct. 19 and that police were "working closely with our partners to investigate."
A cordon has been put in place around Waterglade Industrial Park in Thurrock, which remains closed.