Thirty-nine people have been found dead inside a lorry container at an industrial park in Essex, Sky News reports.
Police and ambulance crews were called following the discovery at Waterglade Industrial Park in Grays at 1.40am.
All 39 people were pronounced dead at the scene and the lorry driver, a 25-year-old man from Northern Ireland, has been arrested on suspicion of murder.
Essex Police Chief Superintendent Andrew Marriner said the vehicle is thought to have come from Bulgaria and entered the UK at Holyhead in Wales on Saturday.
Police have not said where the people who died are from or where they were thought to be travelling to. They said it could take a long time to identify those who have died.
Authorities were warned last year that people smugglers saw the Irish border as a weak point in the UK border and were taking migrants to Ireland before transporting them to Britain. It is not known whether that happened in this case.
Chief Superintendent Andrew Mariner said: ‘This is a tragic incident where a large number of people have lost their lives. Our enquiries are ongoing to establish what has happened.
‘We are in the process of identifying the victims, however, I anticipate that this could be a lengthy process.
‘We believe the lorry is from Bulgaria and entered the country at Holyhead on Saturday, October 19 and we are working closely with our partners to investigate.
‘We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue.’
The investigation will now try to work out where the people who died came from and what route they had taken to get to the UK.
Seamus Leheny, Northern Ireland policy manager for the Freight Transport Association (FTA), said: ‘If the lorry came from Bulgaria, getting into Britain via Holyhead is an unorthodox route.
‘People have been saying that security and checks have been increased at places like Dover and Calais, so it might be seen as an easier way to get in by going from Cherbourg or Roscoff, over to Rosslare, then up the road to Dublin.
‘It’s a long way around and it’ll add an extra day to the journey.’
Richard Burnett, chief executive of the Road Haulage Society, added ‘this tragedy highlights the danger of migrant gangs people-smuggling on lorries’.
Prime Minister Boris Johnson has said he is ‘appalled’ and that his thoughts are with those who lost their lives and their loved ones.
A restaurant worker in the industrial estate, who did not want to be named, said the area was cordoned off by police this morning.
‘There’s a lot of police and forensics,’ the Big Blue Food Bus employee said. ‘We’ve just seen what has been said online. It’s awful. We thought maybe someone had broken into a lorry, but it’s just awful.’
The industrial estate is next to the Dartford Crossing and is used as a stopping point for lorries travelling south to the Port of Dover and the Channel Tunnel, although the planned route of the lorry involved is unknown.
Home Secretary Priti Patel tweeted this morning: ‘Shocked and 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.’
Jackie Doyle-Price, the Conservative MP for Thurrock, tweeted: ‘Sickening news of 39 people found dead in a container in Grays.
‘People trafficking is a vile and dangerous business. This is a big investigation for Essex Police. Let’s hope they bring these murderers to justice.’
Local resident Paige Wade was driving past the industrial park at 4.15 am on the way home from work.
She said: ‘I had just finished work while driving up Motherwell Way and all you could see was blue flashing lights, as I was driving past there was police tape to cordon off the start of the eastern avenue.
‘I knew it was serious because of how many police cars and ambulances were there, but the police had parked their cars across the whole access of the road so you couldn’t see anything.
‘There’s always lorries around there as they park up there for the night, I couldn’t say whether I did or didn’t see the actual lorry in question.’