Police were called by the ambulance service shortly before 01:40 BST after the discovery at Waterglade Industrial Park in Eastern Avenue, Grays, reported BBC.

The lorry driver has been arrested on suspicion of murder.

According to media reports, he has been identified as a 25-year-old man from Northern Ireland.

Essex Police said the vehicle travelled from Bulgaria and entered the country via Holyhead, Anglesey, on Saturday, reported BBC.

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," Mariner said.

"We believe the lorry is from Bulgaria and entered the country at Holyhead on Saturday 19 October and we are working closely with our partners to investigate," he said.

"We have arrested the lorry driver in connection with the incident who remains in police custody as our enquiries continue. 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," he said.

The area has been cordoned off by security forces.

UK PM reacts:

British PM Borish Johnson said he was left appalled by the incident.

"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 tweeted.

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."