One of the biggest murder investigations in British history is underway after 39 bodies were discovered in a lorry container at an industrial estate today.
The lorry driver, a 25-year-old man from Northern Ireland, was arrested and it is thought the HGV travelled from Holyhead, north Wales, across England.
"There is a direct route to Holyhead from Dublin. If the lorry came from Bulgaria, getting into Britain via Holyhead is an unorthodox route," Seamus Leheny, Northern Ireland policy manager for the Freight Transport Association (FTA), said.
Boris Johnson said he is receiving "regular updates" on Essex Police's murder investigation while specialist teams work at Waterglade Industrial Park in Grays .
The bodies, which include that of a teenager, were found there in the red and white lorry's container at around 1.40am.
Dan Peters, from a hydraulic maintenance company on the industrial estate, said it was "terrible" news.
"We’re not able to gain access to our units to open up for daily business," the Pirtek managing director said.
"Obviously, it’s terrible news."
Here is everything we know so far about this appalling tragedy.
When were the bodies found?
Emergency services confirmed they were called to the industrial park at 1.40am this morning.
The 39 people were pronounced dead at the scene.
Since then, officers made the arrest and have continued enquiries.
"We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue," a police spokesman said.
"I appreciate this cordon is going to disrupt the activity of local businesses in the area and we will work to ensure that disruption is kept as short as possible. We are working with Thurrock Council to mitigate against any impact our investigation scene will have locally.”
"A cordon has been put in place and access to and from the Waterglade Industrial Park remains closed."
How did the lorry arrive there?
Police say the lorry, said to be from Bulgaria, entered the county at Holyhead in North Wales on Saturday, October 19.
Ferries sail out of Holyhead port to Dublin in Ireland.
It is the principal link for road vehicles to get from England and Wales to Ireland.
More than two million people travel through the port each year, which is operated by Stena Line Ports Ltd.
Road Haulage Association chief executive Richard Burnett said the lorry could have travelled on a ferry from Cherbourg, France, to Rosslare, Ireland, before driving to Dublin and taking another ferry to Holyhead, North Wales and then reaching Kent by road.
He told PA: "It's highly unlikely that if this vehicle has come from Europe that it's been physically checked.
"Because of the migrant issue at Dover and Calais, you've got far more checks that are taking place there. You've got heartbeat monitors, you've got dogs, you've got CO2. Those checks are done as you drive through.
"Cherbourg, because it's a low volume port, you probably won't have the same security measures that they have in Coquelles, Calais, for the high number of vehicles that are stepping through there and that's been one of the main migrant routes historically.
"If this is somebody trying to smuggle a significant number of people through then maybe Cherbourg has been picked because it's a little easier to get through."
What route did the lorry take?
The container containing the bodies of 39 people was collected in Belfast and then travelled to Dublin, it has been revealed.
The truck travelled down the M1 motorway past Dundalk and Drogheda and on to Dublin in the last few days.
It is suspected that the bodies were in the container was it made its way across the border into the Republic.
It then went through Dublin Port where it experienced no delays and onto the ferry to Hollyhead in Anglesea, Wales.
From there it travelled through the UK to the industrial estate in Essex were it was found.
How have officers been investigating?
Since the young man was arrested, Essex Police continued enquiries.
They've worked with Thurrock Council to help mitigate against any impact our investigation scene.
But access to and from the industrial park remains closed.
Forensic tents and police cars have been pictured at the scene throughout the day.
They continue to appeal for information in the "lengthy investigation".
They also intend to identify the victims in the next stage of the probe.
Has anything like this happened before?
A similar incident happened 19 years ago in Kent.
In June 2000 the bodies of 58 Chinese migrants were found in the back of a lorry in Dover.
Two other migrants survived.
Dutch lorry driver Perry Wacker was convicted of manslaughter in 2001 and jailed for 14 years.
In 2003 nine members of the Chinese snakehead gang - an organised crime group - were jailed for their part in the tragedy.
Who has reacted to the tragic news?
Boris Johnson said he was "appalled" to hear of the tragedy.
The Prime Minister tweeted: "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."
He also said he is receiving "regular updates" on the murder investigation.
Thurrock MP Jackie Doyle-Price 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
“Lets hope they bring these murderers to justice”.
Home Secretary Priti Patel tweeted: "Shocked & 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."
DUP leader Arlene Foster has also tweeted about the tragedy.
She wrote: "Horrifying news coming from Essex this morning. Thinking of those who have impacted and their families during such a distressing time."
What is expected to happen next?
Police said this will be a lengthy process.
The force wants to identify the victims and establish their nationalities.
It continues to appeal for the public's help.