"The identification of the victims remains our number one priority," the Deputy Chief Constable said.

She also requested that if anyone had information about the lorry since it came into the country on 21 October, could they come forward.

Image source, PA Media

Deputy Chief Constable Mills added that the 25-year-old man from Northern Ireland, who was the lorry driver arrested on suspicion of murder, remained in custody.

The Essex Police media conference has begun.

Pippa Mills, Deputy Chief Constable, speaking outside Grays Police Station said "all 39 people inside the vehicle had died".

She said that at this stage the force had not identified where the victims are from.

BBC Essex's Pete Walker is at the scene and told the BBC News Channel: "Behind me is the entrance to a logistics company and not only is there a white and blue police cordon but a green physical barrier.

"It's quite chaotic here and the amount of bystanders and reporters is continuing to grow.

"The industrial estate is huge and has lots of multi-national companies. The nearest residential home must be about half a mile away."

Home Secretary Priti Patel will be giving a statement to the House of Commons later today about the discovery.

She had earlier tweeted that she was "shocked and saddened by this utterly tragic incident".

We await a police press conference which is due to begin at 11:30 and we'll bring you the latest as it happens.

The 39 bodies were discovered in the early hours of Wednesday at Waterglade Industrial Park in Eastern Avenue, Grays.

Essex Police said the lorry was from Bulgaria and entered Wales via Holyhead, Anglesey, on Saturday.

Image source, .

The Waterglade Industrial Park is next to the London Orbital road - mostly designated the M25, but when it approaches the Dartford Crossings under and over the Thames it becomes the A282, because it does not have motorway status for that section.

The Bulgarian newspaper Dnevnik, external is reporting on the discovery of the 39 bodies in Grays.

In its article it quotes a statement credited to the Bulgarian Ministry of Foreign Affairs, which the BBC has yet to speak to.

"Our embassy is in contact with local authorities and is reviewing the case," the statement is quoted as saying.

The lorry was found in the early hours of today on the Waterglade Industrial Park in Grays, where BBC Essex's Richard Smith is.

He said: "Police have cordoned off a large warehouse-type building with blue tape on the industrial estate.

"The scene behind it is hidden by portable privacy screens stretching across an entrance to the site.

"Eastern Avenue is largely quiet this morning, some vehicles are arriving and being turned away."

Shadow Home Secretary Diane Abbott has tweeted about the discovery of the 39 bodies.

"Saddened to hear of the appalling incident involving the deaths of 39 people in the back of lorry in Essex," she wrote. "My thoughts are with the family and friends of those who have died."

DUP leader Arlene Foster also tweeted, saying: "Horrifying news coming from Essex this morning. Thinking of those who have impacted and their families during such a distressing time."

Ellis Whitehouse, a local reporter from the Thurrock Gazette and Echo Newspaper, told BBC Television's Victoria Derbyshire show: "We got the update from police on their media centre this morning.

"I came down here immediately so as it stands I am at the edge of a police cordon into where the crime scene has been discovered.

"I've been told we're going to be allowed access into the site at about 12:30 to have a further look at what is going on inside there, as it's very difficult to tell at the moment."

Essex Police says the force's Deputy Chief Constable Pippa Mills will deliver a statement regarding the murder investigation at Grays Police Station, at 11:30.

We'll bring you the latest from the press conference as it happens.

As we know, Essex Police said it thought that the lorry was from Bulgaria and arrived in Wales, via the port at Holyhead, on Saturday.

Seamus Leheny, Northern Ireland policy manager for the Freight Transport Association, told the Press Association: "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."

BBC Essex reporter Richard Smith has arrived at the Waterglade Industrial Park.

Police say the lorry is from Bulgaria and arrived in Wales, at Holyhead, on Saturday.

The 39 bodies were found at Waterglade Industrial Park, Grays, earlier today.

Dan Peters, from a hydraulic maintenance company on the Waterglae Industrial Park in Grays where the bodies were found, told the Press Association it was "terrible" news.

He said the industrial estate is made up of courier and logistics companies.

"We're not able to gain access to our units to open up for daily business," the Pirtek managing director added.

Essex Police Chief Superintendent Andrew Mariner has said that the cordon in Grays is expected to cause disruption to local businesses, but the force is working with Thurrock Council "to mitigate against any impact our investigation scene will have locally".

Prime Minister Boris Johnson has said he is "appalled" by what has happened and is being regularly updated by the Home Office.

Home Secretary Priti Patel, whose constituency lies in Essex, has tweeted: