London — The bodies of 39 people have been found in a truck in Essex, southeast England. The dead included 38 adults and one teenager, who were discovered in the early hours of Wednesday morning, the Essex Police said in a statement.

The ambulance service was called to Waterglade Industrial Park in Grays, Essex only 22 miles east of central London, where the victims were pronounced dead. The bodies were found in a shipping container on the back of a semi truck parked on the side of the road where police are now conducting their investigation.

The police have launched a murder investigation and have arrested the driver of the truck, a 25-year-old resident of Northern Ireland, on suspicion of murder.

Police and forensic officers investigate a truck in which 39 bodies were discovered in the trailer on October 23, 2019 in Grays, Essex, England. Getty

The police initially said they believed the truck arrived on Saturday from Bulgaria and entered the U.K. at the port in Holyhead, North Wales, more than 300 miles northwest of Essex. According to Bulgarian Prime Minister Boyko Borisov, however the vehicle had not been in Bulgaria since 2017. Reuters reported that the truck was registered in Bulgaria to a company owned by an Irish Citizen.

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British Police later said the truck travelled from Zeebrugge, Belgium into the port at Purfleet near Grays, Essex. The police said they believed the shipping container carried by the truck originated in Ireland.

Deputy Chief Constable Pippa Mills said Wednesday morning that the identification of the victims was the number one priority for the police. She said their nationalities remained unclear.

"This is a tragic incident where a large number of people have lost their lives," Chief Superintendent of Essex Police Andrew Mariner said in the statement.

I’m appalled by this tragic incident in Essex. 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 & their loved ones. — Boris Johnson (@BorisJohnson) October 23, 2019

Prime Minister Boris Johnson said on Twitter he was "appalled" by the incident.

The discovery came two days after British authorities searched properties in Grays, Essex and other locations in the region as part of an ongoing investigation into migrant smuggling.

The British National Crime Agency said in a statement released Monday that five men were arrested in southern England after 13 migrants were found in a truck at the port of Calais, France, on Saturday evening. Neither the Essex Police nor Britain's National Crime Agency were immediately available to comment on any potential connection between the two cases.

In 2001, a Dutch truck driver was convicted of manslaughter for the deaths of 58 Chinese immigrants who suffocated in the back of his tomato truck that was found in Dover, southern England.