Britain launched a major murder investigation after 39 dead bodies were found Wednesday in a refrigerated truck, once again putting the spotlight on the shadowy people trafficking business.

The corpses were found in a truck container at an industrial park in Grays, east of London, triggering outrage among politicians.

The local Essex Police force, which is working with immigration officials, said their initial priority was to try to identify the victims, thought at this stage to be 38 adults and one teenager.

The truck's driver, a 25-year-old man from Northern Ireland, has been arrested on suspicion of murder and remained in custody through Wednesday, the force added.

"This is an unimaginable tragedy and truly heart-breaking," Prime Minister Boris Johnson said.

He said the perpetrators of people smuggling, trading in human lives, "should be hunted down and brought to justice".

Police were called to the scene at the Waterglade Industrial Park at around 1:40am (0040 GMT). Officers in white forensic suits could be seen working by the truck and a white tent was erected outside through the day.

Copyright Agence France-Presse, 2019